Tree Species Selection and Use by Foraging
Insectivorous Passerines in a Forest Landscape
by
Peter S. McKinley
M.S.E.S., Indiana University, 1991
B.A. Colby College, 1987
A Thesis Submitted in Partial Fulfilment of
the Requirements for the Degree of
Doctor of Philosophy
in the graduate academic unit of Biology
Supervisor:
Antony W. Diamond, Ph.D., Department of Biology and
Faculty of Forestry and Environmental Management,
University of New Brunswick.
Examining Board:
John Spray, PhD, Department of Geology
Paul Arp, Faculty of Forestry and Environmental
Management
Steven Heard, Department of Biology
External Examiner:
Richard Holmes, Ph.D., Department of Biology, Dartmouth
College, New Hampshire, USA.
This thesis is accepted.
______________________
Dean of Graduate Studies
THE UNIVERSITY OF NEW BRUNSWICK
July, 2003
 Peter S. McKinley,
Dedication
Dedicated to my parents, Robert S. and Carol E. McKinley, an ever present source of
passion, curiosity, encouragement, and love, and in loving memory of my brother,
Andrew S. McKinley, Andy, 1966-1996. Your kindness, courage, and love are a bright
light and constant source of motivation, strength, and will. You are remembered and
loved always.
ii
Abstract
Tree species were selectively used or avoided by foraging songbirds in a northern
temperate mixed-wood forest. American beech (Fagus grandifolia) was selected out of
proportion to its abundance by the black-throated green warbler (Dendroica virens)
during several years of the four year study. Black-throated blue warblers (Dendroica
caerulescens), American redstart (Setophaga ruticilla), and least flycatcher (Empidonax
minimus) also showed selective foraging use of the American beech. Yellow birch,
(Betula alleghaniensis) was usually avoided by these same birds. Selective foraging
occurred in sugar maple in a stand with a history of intensive forest management that had
resulted in the virtual absence of American beech.
Rates of foraging differed significantly among tree species in some years for the
black-throated blue and black-throated green warblers, but the results were less consistent
than the selective use results. The black-throated green warbler showed significantly
higher rates of foraging in the American beech versus yellow birch in two years. The
black-throated green warbler also showed a higher ratio of attacks per flight in the
American beech. This measure is interpreted as the number of attacks per foraging patch.
I defined the patch as the length of branch searched by a bird hopping in between short
flights within the same tree.
I collected data on the birds’ stomach contents to confirm that the avian diet was
represented in the arthropod samples that I collected from the various tree species. The
arthropod hypothesis predicts that differences in arthropod density or diversity among
tree species drives selective foraging behaviour. Arthropod density and diversity did not
iii
differ among tree species in a pattern that would explain the selective foraging behaviour
of the focal bird species. The tree species that tended to have higher abundances of
arthropods (yellow birch) was usually avoided by the foraging birds. The tree
morphology hypothesis focuses upon an optimal relationship between a tree species’
structure and a bird’s foraging behaviour. This process is probably responsible for the
differential patterns of use among tree species in this study. This research offers the first
evidence for the sole function of one of the explanatory hypotheses in a deciduous forest
system.
Based on the role played by American beech as a foraging substrate, its
availability was regressed on avian presence/absence data. American beech basal area
predicted landscape patterns of distribution of one focal species, black-throated green
warbler, and two non-focal species, northern parula and magnolia warbler.
Finally, patterns of foraging behaviour were compared with landscape patterns of
productivity for the black-throated green warbler. American beech basal area was a
significant predictor of avian productivity in a companion study. This suggests that
patterns of foraging behaviour by individual birds can be “scaled up” to predict spatial
patterns in distribution of productivity across the landscape.
Whereas previous work has established the importance of tree species diversity to
avian foraging ecology, this research documents the importance of morphological
diversity within deciduous tree species. Previous ambiguity about causal processes
responsible for selective foraging patterns in tree species has been eliminated. This work
also demonstrates the dynamic nature of avian foraging ecology across a region that
iv
includes the same bird and tree species. Caution is warranted in extrapolation of results,
even within similar forest systems.
v
Acknowledgements
First and foremost, I wish to express deep gratitude to my advisor, Tony Diamond. His
patience, humanity, and science are exceptional and have helped to sustain me on this
long trip. I also wish to thank my committee members, Graham Forbes, Marc-Andre
Villard, and Gerry Parker for their insight and guidance throughout this project. Thanks
also to the University of New Brunswick Biology Department and especially Tim
Dilworth, Tillmann Benfey, Dion Durnford, and Linda Allen for their support and
assistance. I also wish to thank my field assistants, Daniel Mazerolle, Trista Michaud,
Jaime Glenn, and Karen Gosse for their hard work and companionship through many
hours in the field and field camp. Thanks also to Rhonda Hudson and again to Jaime
Glenn for their help on this project in association with their honours theses. I would also
like to express my appreciation to Fraser Papers Inc. and specifically to Gilles Couturier
and Steve Young. Thanks also to John Gunn, Jeff Bowman, and Mark Edwards for their
many contributions including friendship and moral support. This study was funded by
grants to A.W. Diamond from the Sustainable Forest Management Network of Centres of
Excellence and Natural Sciences and Engineering Research Council of Canada
(NESERC), and the Atlantic Cooperative Wildlife Ecology Research Network
(ACWERN)
vi
Table of Contents
Abstract…………………………………………………………………………………..iii
List of Tables………………………………………………………………………….….3
List of Figures………………………………………………………………………….…6
List of Plates…………………………………………………………………………. .…9
List of
Abbreviations………………………………………………………………….………....10
Chapter 1: Introduction………………...……………………………………………….. 11
Research Questions…………………………………………………………………..11
Macro-scale (Habitat) Vegetation Structure…………………………………………13
Floristic Diversity and Micro-Scale Vegetation Structure…………………………..14
Landscape Pattern and Process………………………………………………………21
Chapter 2: Methods…………………………………….………………………………...27
Study Area and General Sampling Design…………………………………………..27
Grid Vegetation Sampling…………………………………………………………...30
Foraging Behaviour………………………………………………………………….31
Diet Composition………………………………………………………………….…36
Arthropod and Tree Species Associations…………………………………………..38
Landscape Distribution and Productivity…………………………………………...40
Chapter 3: Foraging Behaviour Results………………………………………………...47
Foraging Behaviour Overview……………………………………………………..47
Foraging Site Selection ……………………………………………………………48
Forage Rate………………………………………………………………………..51
Forage Manoeuvre ……………………………………………………………….53
1
Diet Composition…………………………………………………………………54
Chapter 4: Arthropod Prey Density and Diversity Results…………………………...73
Chapter 5: Landscape Distribution and Productivity Results…………………………91
Chapter 6: Discussion, Consclusions, and Management Implications……………….97
Foraging Site Selection and Success………………………………………………97
Evaluation of the Arthropod Hypothesis…………………………………………102
Evaluation of the Morphology Hypothesis………………………………………104
Landscape Pattern and Process…………………………………………………..111
Regional Comparison……………………………………………………………112
Forest Management……………………………………………………………..116
Future Research…………………………………………………………………118
Appendix I………………………………………………………………………….125
References Cited……………………………………………………………………128
Vita…………………………………………………………………………………141
2
List of Tables
Table 2.1. Relative Proportions of the four focal tree species on each grid………….…43
Table 3.1. Number of observation sequences by grid, bird species, and year
with mean duration of sequence and standard error (SE)…………………………..56
Table 3.2. Number of attacks each season by bird and tree species, and mean
number of attacks per observation sequence with standard error SE by grid
and year……………………………………………………………………………..57
Table 3.3. Goodness of fit analysis for foraging use versus availability of
the four focal tree species combined……………………………………………….58
Table 3.4. Multiple comparison of forage attacks per minute by btgw
(Nemenyi test p<0.05) for differences among tree species, 1996
reference grid……………………………………………………………………..59
Table 3.5. Multiple comparison of forage attacks per minute by btgw
(Mann-Whitney p < 0.05) for differences among tree species,
1999 reference grid……………………………………………………….………59
Table 3.6. Multiple comparison of forage attacks per minute by btbw
(Mann-Whitney test p<0.05) for differences among tree species,
1996 reference grid………………………………………………………………60
3
Table 3.7. Multiple comparison of forage attacks per flight by btgw
(Mann-Whitney U-test p<0.05) for differences among
tree species, 1999 reference grid…………………………………………….………60
Table 3.8. Multiple comparison of forage attacks per flight by btgw
(Mann-Whitney U-test p<0.05) for differences among
tree species, 1996 reference grid…………………………………………………..60
Table 3.9 Attack manoeuvres by tree species and bird species,
all years combined, reference grid only……………………………………………61
Table 3.10. Goodness of fit analysis for forage manoeuvres among tree
species………………………………………………………………………………61
4
Table 4.1. Number, mean, and standard error of occurrence (SE) of
arthropod orders for reference grid 1998…………………………. ………………. 75
Table 4.2. Number, mean, and standard error of occurrence (SE) of
arthropod orders for reference grid 1999………………………………. …..……...76
Table 4.3. Number, mean, and standard error of occurrence (SE) of
arthropod orders for managed grid 1999………………………….. .………………77
Table 4.4. Significant (p<0.05) Bonferonni post-hoc pair-wise comparisons of
arthropod variables, data based on number per unit leaf area………………………78
Table 4.5 Significant (p<0.05) Bonferonni post-hoc pair-wise comparisons of
arthropod variables, data based on clip sample……………………………………..79
Table 4.6 Number and area of leaves per clip sample………………………………….80
Table 5.1. Logistic regression of bird presence on tree basal area…………………... 96
5
List of Figures
Figure 2.1. New Brunswick study site location………………………………………...44
Figure 2.2. Schematic diagram of research grid design…………………………………45
Figure 2.3. Schematic diagram of vegetation sampling plots………………………….. 46
Figure 3.1. Least flycatcher and black-throated blue warbler expected and observed
foraging use, im-grid……………………………………………………………...…62
Figure 3.2. Black-throated green warbler expected and observed foraging use,
im-grid……………………………………………………………………………….63
Figure 3.3. American redstart expected and observed foraging use, mm-grid………….64
Figure 3.4. Least flycatcher expected and observed foraging use, mm-grid……………65
Figure 3.5. Black-throated blue warbler expected and observed foraging use,
mm-grid……………………………………………………………………………66
Figure 3.6. Black-throated green warbler expected and observed foraging use,
mm-grid…………………………………………………………………………...67
Figure 3.7. Black-throated green warbler expected and observed use of hover and glean
forage manoeuvre…………………………………………………………………68
Figure 3.8. Black-throated blue warbler expected and observed use of hover forage
manoeuvre…………………………………………………………………………69
Figure 3.9. American redstart expected and observed use of hover and glean forage
manoeuvres…………………………………………………………………….….70
Figure 3.10. Least flycatcher expected and observed use of hover and hawk forage
manoeuvre…………………………………………………………………………71
Figure 3.11. Proportional occurrence of arthropod orders in stomach contents……...72
6
Figure 4.1. Araneida individuals per clip sample by tree species
on the reference grid in 1999………………………………………………………..81
Figure 4.2. Coleoptera individuals per clip sample
by tree species on the reference grid in 1999………………………………...…81
Figure 4.3. Total arthropod density per clip sample
by tree species on the reference grid in 1999…………………………………..82
Figure 4.4. Araneida density per square centimetre of
leaf area by tree species on the reference grid in 1999…………………………82
Figure 4.5. Coleoptera density per square centimetre of
leaf area by tree species on the reference grid in 1999…………………………83.
Figure 4.6. Total arthropod density per square centimetre of
leaf area by tree species on the reference grid in 1999…………………………83
Figure 4.7. Coleoptera density per square clip sample
by tree species on the managed grid in 1999…………………………………..84
Figure 4.8. Total arthropod density per clip sample
by tree species on the managed grid in 1999……………………………….…84
Figure 4.9. Coleoptera density per square centimetre
of leaf area by tree species on the managed grid in 1999……………………...85
Figure 4.10. Hymenoptera density per square centimetre
of leaf area by tree species on the managed grid in 1999…………………..…85
Figure 4.11. Total arthropod density orders per square
centimetre of leaf area by tree species on the managed grid in 1999…………86
Figure 4.12. Coleoptera density per clip sample
by tree species on the reference grid in 1998…………………………………86
7
Figure 4.13. Order richness per clip sample by tree species on
the reference grid in 1998……………………………………………………….87
Figure 4.14. Arthropod density per clip sample by tree species
on the reference grid in 1998…………………………………………………….87
Figure 4.15. Araneida density per square centimetre of leaf area
by tree species on the reference grid in 1998…………………………………....88
Figure 4.16. Coleoptera density per square centimetre of leaf area
by tree species on the reference grid in 1998………………………………..…..88
Figure 4.17. Hymenoptera density per square centimetre of leaf area
by tree species on the reference grid in 1998……………………………….…...89
Figure 4.18. Diptera density per square centimetre of leaf area
by tree species on the reference grid in 1998……………………………………89
Figure 4.19. Arthropod richness per square centimetre of leaf area by
tree species on the reference grid in 1998………………………………………90
Figure 4.20. Arthropod density per square centimetre of leaf area by
tree species on the reference grid in 1998………………………………………90
8
List of Plates
Plate 6.1. American beech branch and twig morphology within approximately 1 m3
foraging patch, total leaf area: 3224 cm2..………………………………………….119
Plate 6.2. Yellow birch branch and twig morphology within approximately 1 m3 foraging
patch, total leaf area: 1550 cm2……………………………………………………..120
Plate 6.3. Sugar maple branch and twig morphology within approximately 1 cubic meter
foraging patch, total leaf area: 2860 cm2…………………………………………..121
Plate 6.4 Yellow birch (left) and American beech branch, twig, and leaf morphology
removed from tree……………………………………………………………….…122
Plate 6.5 Sugar maple (left) and American beech branch, twig, and leaf morphology
removed from tree………………………………………………………………….122
Plate 6.6 American beech branch morphology on tree………………………..……….123
Plate 6.7 Yellow birch branch morphology on tree………………………………..….123
Plate 6.8 Sugar maple branch morphology on tree………………………..…………..124
9
List of Abbreviations
Please refer to the following guide for interpretation of abbreviations used in the tables
and graphics:
Tree Species:
ambe – American beech (Fagus grandifolia)
yebi – yellow birch (Betula alleghaniensis)
suma – sugar maple (Acer saccharum)
bafi – balsam fir (Abies balsamifera)
Bird Species:
amre – American redstart (Setophaga ruticilla)
lefl – least flycatcher (Empidonax virens)
btbw – black-throated blue warbler (Dendroica caerulescens)
btgw – black-throated green warbler (Dendroica virens)
mnwa – magnolia warbler (Dendroica magnolia)
scta – scarlet tanager (Piranga olivacea)
yrwa – yellow rumped warbler (Dendroica coronata)
revi – red-eyed vireo (Vireo olivaceus)
bhvi – blue-headed vireo (Vireo solitarius)
cswa – chestnut-sided warbler (Dendroica pensylvanica)
nopa – northern parula (Parula americana)
phvi – Philadelphia warbler (Vireo philadelphicus)
Arthropod Orders:
aran – Araneida
cole –Coleoptera
hyme – Hymenoptera
dipt – Diptera
lepi – Lepidoptera
tric – Trichoptera
homo – Homoptera
hemi – Hemiptera
tric – Trichoptera
Research Grids:
mm-grid – moderately managed grid
im-grid – intensively managed grid
10
Chapter 1: Introduction
Research Questions
Historic concentration on the importance of habitat or vegetation macro-structure
has left the realm of avian foraging behaviour in relation to floristic diversity still
relatively poorly understood, especially with respect to causal processes (Whelan 2001
and see reviews below). This dissertation examines how tree species affect arboreal
insectivore foraging behaviour. Previous work (Holmes and Robinson 1981, Robinson
and Holmes 1984) has not been able to distinguish between the two primary causal
processes proposed to explain selective foraging in deciduous tree species.
The ‘arthropod’ hypothesis predicts that abundance or diversity of arthropod prey
on a tree species determines avian selection of that tree species. The ‘morphology’
hypothesis predicts that the foraging strategy of a bird species is adapted to the fine-scale
differences in structure of particular tree species (Morse 1976, Greenberg and Gradwohl
1980, Holmes and Robinson 1981, Morrison et al. 1985). One of my goals is to better
understand the relative contributions of these two processes to tree species-specific
selective foraging patterns among birds. No clear distinction between these two
hypotheses has been established for selective avian foraging patterns in deciduous tree
species.
This dissertation also explores for the first time how a birds’ use of a tree
species as a foraging patch may be scaled up to explain landscape patterns of
avian productivity and distribution. This type of work is an answer to calls made
for a clearer understanding of the relationship between landscape pattern and
11
Comment [TD1]: Does ‘landscape
distribution’ mean distribution of landscape
elements (e.g. habitat patches)? OR
distribution of birds about the landscape? If
the latter, I suggest deleting the word
‘landscape here; then its clear your
comparing bird productivity & distribution
at the landscape scale.
process (Wiens 1995, Lima and Zollner 1996, South et al. 2001, Morales and
Ellner 2002, Wu and Hobbs 2002). Recent work has examined behavioural
processes in the context of landscape questions (Lambert and Hannon 2000,
Mortberg 2001, Belisle and Desrochers 2002, Gobeil and Villard 2002, Belisle
and Desrochers 2002, Robichaud et al. 2002, and see reviews below), but no other
work attempts to scale foraging behaviour up to landscape pattern and process.
My work allows an examination of avian foraging ecology at an even
larger spatial scale when I compare and contrast it to the work of Holmes and
Robinson (1981) in New Hampshire, several hundred kilometres away from my
New Brunswick study sites. Parrish (1995b) offered a similar comparison in his
study of coastal Maine and inland New Hampshire birds. Such comparisons
highlight behavioural differences possibly due to genetic variation within the
region-wide meta-population (as with Parrish 1995b) or due to regional
differences in the arthropod prey base.
Other components of my work examine the impact of stand diversity
simplification due to commercial forest management on avian foraging behaviour.
Previous work in avian foraging ecology (Holmes and Robinson 1981, Whelan
2001) has suggested, but not tested the potential impacts of reducing tree species
diversity on avian foraging behaviour.
12
Macro-scale (Habitat) Vegetation Structure
Wiens (1989) argued that most work on avian habitat selection and use
emphasizes the importance of macro-scale vegetation structure rather than species
composition. Neglect of vegetation floristic composition is evident in influential work
spanning four decades (MacArthur and MacArthur 1961, Karr and Roth 1971, Anderson
and Shugart 1974, Willson 1974, Cody 1981, James and Wamer 1982, Wahlter 2002).
This emphasis can be traced to the early work of MacArthur and MacArthur (1961), who
found that plant species diversity and foliage height diversity were good predictors of
bird species diversity. Plant species diversity and foliage height diversity were correlated
and they saw no independent role for plant species diversity apart from its contribution to
foliage height diversity, though they could plausibly have argued the opposite. Morse
(1985) concluded that though foliage height distributions are often variables in
multivariate models, they contribute little to explaining the variance in distributions of
birds. Wiens (1989) suggested that the relative ease of measurement of structural
variables over floristic variables may have further contributed to the dominance of this
trend in past research.
13
Floristic Diversity and Micro-Scale Vegetation Structure
Other work has nevertheless demonstrated that plant species composition is
important to generalized selection and use of habitat by birds (Morse 1977, 1978,
Franzreb 1978, Holmes et al. 1979, Beedy 1981, James and Wamer 1982, Anderson et al.
1983, Morrison and Meslow 1983, Rice et al. 1983, Abbott and Van Heurck 1985,
Virkkala 1988). More specifically, a few studies have demonstrated selective use of tree
species by foraging birds (Morse 1971, 1976, Holmes and Robinson 1981, Robinson and
Holmes 1984, Airola and Barrett 1985, Cumming 1994, Robichaud and Villard 1999,
Greenberg et al. 2001, Whelan 2001).
Morse (1968, 1971, 1976) observed warblers foraging in white spruce (Picea
glauca) and red spruce (Picea rubra). His data set included arthropod abundance in the
tree species, avian diet composition, avian foraging behaviour, and examination of finescale foliage structure. He found that black-throated green warblers (Dendroica virens)
selectively foraged in red spruce in spite of lower insect biomass in that tree species.
Morse (1976) proposed that the longer red spruce branches would provide a greater
surface of substrate to search in between inter-branch flights. Red spruce branches might
also be easier to traverse while foraging due to acute angle needle orientation as opposed
to right angle orientation of white spruce (Morse 1976).
Holmes and Robinson (1981) found that seven bird species including the blackthroated green warbler foraged selectively in yellow birch (Betula allegheniensis) on
their New Hampshire study site. They also demonstrated selective avoidance of sugar
maple (Acer saccharum), and American beech (Fagus grandifolia) by most of the same
bird species. They found higher arthropod abundance in the yellow birch than in
14
American beech and sugar maple. They also they also argued that yellow birch had a leaf
and branch morphology most conducive to efficient avian foraging. There are no cases
where selective foraging occurred in a tree species with sub-optimal (according to the
investigators’ definitions) leaf and branch arrangement coupled with optimal arthropod
resources. Similarly there were no cases where selective foraging occurred in a tree
species with optimal (according to the investigators’ definitions) leaf and branch
arrangement coupled with sub optimal arthropod resources (Holmes and Robinson 1981,
Robinson and Holmes 1984, Holmes and Schultz 1988).
Previous research on foraging manoeuvres has addressed the relationship between
forage manoeuvre and time of season (Miles 1990, Lovette and Holmes 1995), forage
manoeuvre differences among congeners (James 1976, Holmes and Robinson 1984),
forage manoeuvre in breeding vs. wintering grounds (Lovette and Holmes 1995), and the
relationship between forage tactics and vegetation community structure (Maurer and
Whitmore 1981). Differential use of forage manoeuvres by insectivorous passerines in
particular tree species has been documented in a northern hardwood forest similar to my
own study sites and for some of the same bird species (Robinson and Holmes 1982,
Robinson and Holmes 1984, Holmes and Schultz 1988).
I selected black-throated blue warbler (Dendroica caerulescens), black-throated
green warbler, American redstart (Setophaga ruticilla), and least flycatcher (Empidonax
minimus) for my research. The four neotropical migrant species are arboreal insectivores
that demonstrate varying degrees of reliance upon the various foraging attack strategies
(Morse 1993, Briskie 1994, Holmes 1994, Sherry and Holmes 1997). Such varied
responses to micro-scale vegetation structure are likely to provide a good model system
15
for elucidation of selective foraging causal processes in relation to micro-scale vegetation
differences.
Morse (1993) found that black-throated green warblers glean over 80% of the
time, and use the hover manoeuvre only 10% of the time in predominantly softwood
forests. Robinson and Holmes (1982) found black-throated green warblers using the
glean and hover manoeuvres 54% and 35% of the time respectively in their
predominantly hardwood study site and recorded the hawk manoeuvre only 2% of the
time. Black-throated blue warblers used the glean and hover manoeuvres 33% and 61%
of the time respectively, and used the hawk manoeuvre 4% of the time (Robinson and
Holmes 1982). These congeners offer a potential contrast in their use of foliage microstructure due to their foraging strategy differences. The third warbler, American redstart,
used the glean manoeuvre 23 % of the time and used the hover manoeuvre 53 % of the
time (Robinson and Holmes 1982). Use of the glean by American redstarts was less
frequent than either Dendroica species and its use of the hover was intermediate.
American redstarts used the hawk manoeuvre 6% of the time, slightly more often than the
two Dendroica species (Robinson and Holmes 1982). Least flycatchers used the glean
manoeuvre the least of all, 3% of all forage manoeuvres, and used the hover and hawk
manoeuvres more than the other species, 81% and 10% of the time respectively
(Robinson and Holmes, 1982).
The patterns above represent responses pooled over all tree species, implying an
overall optimal strategy for each bird species. A finer scale of analysis reveals that
foraging strategies can be affected by tree species. Holmes and Schultz (1988) reported
that black-throated green warblers used the glean manoeuvre most frequently on
16
American beech and least frequently on sugar maple, while it used the hover manoeuvre
most frequently on sugar maple and approximately equally on American beech and
yellow birch. Black-throated blue warblers used the glean most frequently on yellow
birch and approximately equally on sugar maple and American beech, while it used the
hover manoeuvre least frequently on yellow birch and approximately equally on sugar
maple and American beech. American redstarts used the hover and glean manoeuvres
approximately equally in American beech, sugar maple and yellow birch. Robinson and
Holmes (1984) showed similar results in their analysis that differentiated the vegetation
into canopy, subcanopy, and understory layers.
More recent field-based work has continued to confirm patterns of selective
foraging in tree species but has not addressed causal processes. Robichaud and Villard
(1999) demonstrated selective foraging and singing by black-throated green warblers in
white spruce (Picea glauca) and selective foraging in trembling aspen (Populus
tremuloides) and balsam poplar (Populus balsamifera). Greenberg et al. (2001) observed
that black-throated green warblers did not select particular tree species for their foraging
activity on their wintering sites in Mexico. This species did, however, show the greatest
degree of specialization in its foraging strategies. The other two species in his study,
Townsend’s warbler (Dendroica townsendi) and hermit warbler (Dendroica occidentalis)
demonstrated strong selective use of pine and weak selective use of oak (Greenberg et al.
2001). Their study did not measure the prey available, so determination of the process
driving the foraging site selection was not possible. The authors speculated that bird and
tree morphology probably played strong roles in the evolution of this genus.
17
Parrish (1995a) offered experimental tests of some of Morse’s (1976) predictions
concerning white and red spruce needle and branch morphology effects on bird foraging
behaviour. He found that manipulating white spruce needle angles to resemble red
spruce angles resulted in higher proportions of prey taken from this substrate versus
controls. Decreasing white spruce needle length to approximate red spruce needles
resulted in increases in prey proportions taken and time spent in this species versus
controls (Parrish 1995a).
In other experimental aviary work Parrish (1995b) took advantage of regional
differences in foliage use by black-throated green warblers. Individuals from New
Hampshire select deciduous foliage, while coastal Maine individuals select coniferous
foliage for foraging and displaying. He experimentally increased the prey for each
species on the less favourable tree type. The birds from each regional population selected
the less favourable tree type for foraging while maintaining the original tree type for
display activities. He took a variety of morphological measurements from individuals of
each population and found significant differences in maxillar width, tibiotarsi,
tarsometatarsi, humeri, and radii. He concluded that morphological variation within a
species could be responsible for intrinsic microhabitat preferences across a region
(Parrish 1995b).
Gunnarson (1996) employed experimental manipulation of spruce needle density
to demonstrate the importance of fine scale tree morphology to foraging insectivores.
One particularly interesting effect might have implications for my own work with
naturally varying leaf densities among deciduous trees. In one trial, he observed lower
18
effects of bird predation on arthropod density on tree branches with needle density
experimentally reduced.
Whelan (2001) employed experimental methods with broad-leaved trees and
insectivorous passerines to demonstrate the influence of fine-scale tree morphology to
foraging insectivores. Black-throated blue warblers, black-throated green warblers, and
Comment [TD2]: Scientific name here
American redstarts captured more prey from the upper surfaces of yellow birch (Betula
alleghaniensis). Black-throated blue warblers and American redstarts captured more
prey from lower leaf surfaces of sugar maple (Acer saccharum), while black-throated
green warblers captured more prey from upper leaf surfaces of sugar maple. Yellow
birch has leaves within the same plane as the branch, while sugar maple has leaves
elevated above the branch (Whelan 2001). Further experimentation demonstrated that
leaf dispersion is responsible for leaf surface use, and distance to prey is responsible for
whether the prey manoeuvre is aerial or non-aerial.
In related work, Whelan (1989a) demonstrated that black-throated green warblers
displayed a greater learning efficiency for locating prey on leaf undersides. Blackthroated blue warblers displayed a greater learning efficiency for locating prey on leaf
upper sides . Interestingly, the foliage structure of yellow birch and sugar maple had no
effect on the birds’ ability to locate prey.
Comment [TD3]: A bad case of nounstringing! Try ‘the birds’ ability to learn the
location of prey’
Whelan (1989b) used an experimental design to control prey available on
simulated branches and foliage of sugar maple and yellow birch. Black-throated
blue warblers selected distal sugar maple foliage over yellow birch when prey
biomass was equal. Black-throated blue warblers selected yellow birch when the
biomass on this foliage was increased. Black-throated green warblers showed no
19
selection between these same two foliage patterns when biomass was equivalent,
but did select yellow birch when biomass was increased. However, the increase
in biomass needed to shift the black-throated green warbler selection was greater
than the biomass needed for black-throated blue warblers.
20
Landscape Pattern and Process
I started this project at a time when landscape ecology was replete with studies of
pattern rather than causal processes (see review in Wiens 1995). Lima and Zollner
(1996) suggested that models of animal behaviour should be used to explain landscape
patterns and processes. South et al. (2001) echoed this need for more landscape research
directed at behavioural mechanisms. Morales and Ellner (2002) concluded that
movement models that incorporate behavioural heterogeneity were more powerful in
predicting dispersion than models of landscape structure. Wu and Hobbs (2002) report a
better understanding of landscape process in relation to landscape pattern among the
“Top 10 List for Landscape Ecology in the 21st Century” developed at the 16th Annual
Symposium of the US Regional Association of International Association of Landscape
Ecology.
Fragmented landscapes have been well studied in the interest of
conservation and the opportunities they offer for experimental approaches to basic
research (Lynch and Whitcomb 1978, Villard et al. 1993, Hagan et al. 1996,
Wiens 1996, Diamond 1999, Lambert and Hannon 2000, Belisle and Desrochers
2002, Robichaud et al. 2002). Early work on landscape fragmentation often
involved applied concepts of island biogeographic theory (MacArthur and
Wilson 1967). Patterns of species diversity and abundance in fragmented
landscapes have been related to patch area (Forman et al. 1976, Galli et al. 1976,
Ambuel and Temple 1983, Freemark and Merriam 1986, Robbins et al. 1989,
Freemark and Collins 1992, Wiens 1996), and patch isolation (MacClintock et al.
1977, Lynch and Whitcomb 1978, and Urban et al. 1988, Litwin and Smith 1992,
21
Villard et al. 1992, and Gilpin 1996).
A common theme in early studies of landscape process focused on habitat edge
dynamics and avian nest predation effects upon reproductive success (Gates and Gysel
1978, Kroodsma 1982, Brittingham and Temple 1983, Wilcove 1985, Harris 1988,
Robinson et al. 1995, Lidicker and Koenig 1996, Bayne and Hobson 1997). These
studies represent an examination of causal process in a landscape pattern, but do not
delve into behavioural processes of a single species.
The study of pairing success in fragmented landscapes represents a
behavioural approach focused on the autecology of a single species. This process
is associated with isolation and reduced area of individual patches (Porneluzi et
al. 1993, Villard et al. 1993, Hagan et al. 1996, Lambert and Hannon 2000). A
variety of studies have addressed landscape processes and resource quality,
though they have not explicitly related foraging behaviour to landscape pattern or
process. Holmes et al. (1992) demonstrated that population recruitment can be
influenced by the availability of arthropod prey at Hubbard Brook, thus
establishing a process whereby arthropod availability might influence productivity
and population distribution across the landscape.
Mazerolle and Hobson (2001)
were interested in the relative physiological stresses experienced by territorial
birds in fragments and contiguous forest. Their work focused on territorial
defence rather than foraging ecology. They found that larger and more
competitive males settled more densely in the contiguous forest and experienced
higher stress in defence of their territories. This is a good example of the
interplay between behaviour and landscape pattern.
22
Johnson and Sherry (2001) related arthropod prey distribution to
landscape distribution of warblers on their winter grounds in Jamaica. They did
not relate these patterns to forest fragmentation and foraging behaviour, and could
not relate the patterns to reproductive success. Zanette et al. (2002) documented
lower densities of arthropod prey available to an insectivorous passerine and
subsequent lower reproductive success in fragments vs. contiguous forest in
Australia. While this study simultaneously addressed resource quality,
fragmentation, and reproductive success, it did not include a study of foraging
behaviour. Mortberg (2001) investigated the contribution of tree species to
habitat quality and landscape pattern as perceived by nuthatches. The birds
showed a positive association with oak in landscape patches. The association was
based on census data and did not address such causal processes as foraging.
Belisle and Desrochers (2002) experimented with gap crossing behaviour
of forest birds and not only demonstrated gap avoidance, but quantified effective
gap size. Hinsley (2000) related gap crossing to body mass, flight speed and
brood size of the great tit (Parus major). Matthysen (2002) related great tit and
blue tit (Parus caeruleus) dispersal to natal territory position within a patch.
Robichaud et al. (2002) demonstrated the dynamic reversible quality of a gap
through time as a clearcut forest regenerated. Movement rates of adults increased
in adjacent buffer strips following the harvest. After only four years of
regeneration, movement rates of dispersing juveniles increased in the clearcut.
Gobeil and Villard (2002) performed experimental translocations of two
bird species to examine landscape permeability with respect to forest cover. The
23
ovenbird was selected for its association with closed canopy hardwood stands
while the white-throated sparrow (Zonotrichia albicollis) uses a variety of age
classes and stand compositions. Ovenbird movement was facilitated by the
presence of forest cover while white throated sparrow movement was optimal in
Comment [TD4]: How did WTSP
respond? Having mentioned them, you
should not leave us in suspense..!
harvested and agricultural landscapes.
In spite of significant advances that establish linkages among behavioural
processes and landscape pattern, and independent work examining the role of
floristic composition in foraging ecology, the two approaches have remained
separate. Studies of landscape pattern and habitat selection by birds continue to
describe vegetation cover types in broad terms and fail to investigate causal
processes (Freedman et al. 1981, Spies et al. 1994, McGarigal and McComb
1995, Willson and Comet 1996, Farina 1997, Hagan et al. 1997, Jansson and
Angelstam 1999, Howell et al. 2000, Penhollow and Stauffer 2000, Jones and
Robertson 2001, Wolter and White 2002).
Such work documenting extremes on a continuum of predictor variables
such as hardwood vs. softwood are valuable first approximations. Personal
involvement in one of these studies (Hagan et al. 1997) leaves me with no doubt
about the need to simplify the experimental design when looking for broad
patterns. The next logical step is to incorporate more natural complexity into our
work as we attempt to understand causal landscape processes.
This dissertation relates selective foraging in tree species to songbird
landscape distribution and productivity to establish the importance of local
behavioural processes in landscape pattern and dynamics. Previous work has
24
related foraging behaviour and habitat selection, but at limited temporal and
spatial scales within homogeneous landscape patches rather than across the
mosaic (Sherry and Holmes 1979) or across isolated islands in a coastal landseascape rather than a strictly terrestrial mosaic (Morse 1976). Sherry and
Holmes (1979) used ordination techniques to relate avian community structure to
intra-patch distributions of those tree species selected by foraging birds. Sherry
and Holmes (1985) describe the scale of their work as encompassing one habitat
type. This work did not address larger temporal and spatial scales associated with
seasonal landscape settlement. Orians (1991) makes distinctions among different
types of habitat selection based upon the spatial scale of an animal’s behaviour.
At the largest scale, he describes habitat selection as a function of emigration,
immigration, and migration. I use local foraging patterns to predict a landscape
settlement pattern.
I continue my investigation of the role local behavioural processes play in
landscape dynamics in conjunction with that of my colleague working
simultaneously on the same study site (Gunn 2002). I relate local foraging
behaviour and tree species composition to landscape patterns of reproductive
success documented by Gunn (2002). While this component of my work is more
suggestive than conclusive, such a scaling up of a behavioural process to
landscape pattern of productivity has not previously been demonstrated.
Whelan (2001) and Holmes and Robinson (1981) argue for the
maintenance of native tree species diversity in managed forests in light of the
unique foraging opportunities offered by different tree species. I was able to
25
compare bird foraging behaviour in moderately managed and intensively
managed landscapes to document the effects of simplifying the tree species
composition. My work also offers the first look at a region-wide comparison of
foraging behaviour differences similar to the work of Parrish (1985b) comparing
tree species selection differences between coastal and inland populations of a
warbler species. The bird and tree species that are discussed in this dissertation
included the same species studied in the most comprehensive work to date on this
subject (Holmes and Robinson 1981, Robinson and Holmes 1984, Holmes and
Schultz 1988), yet the results of their studies and mine differ in important ways.
The only other work (Block 1988) that made a regional comparison of tree
species use did not compare the two causal processes.
26
Chapter 2 Methods
Study Area and General Sampling Design
My work was conducted in the Appalachian highlands of northwestern
New Brunswick, Canada. The study site (Figure 2.1) is located west of the
Tobique River (47 N, 67 W) on freehold land managed by Fraser Papers Inc.
The field work for this dissertation was conducted in the upland stands.
We selected two 4900 ha study landscapes to represent the two extremes found in
commercially managed forest. One of these landscapes was chosen for its maximal area
of mature secondary mixed-wood forest not scheduled to be harvested for the duration of
the project, approximately 4 years. Less than 15% of this landscape was in young
plantation or recent clearcuts. This served as a reference landscape (mm-grid) for
comparison with the second 4900 ha landscape, the intensively managed area (im-grid).
Over 50% of this landscape was covered by young regenerating clearcut or softwood
plantation.
American beech (Fagus grandifolia), yellow birch, and sugar maple were
the dominant upland overstory species in the mm-grid, while yellow birch and
sugar maple were the dominant upland overstory species in the im-grid. American
beech was a minimal component of the im-grid (Table 2.1). Please see Table 2.1
for relative proportions of tree species in the two grids. Balsam fir (Abies
balsamifera) and white spruce, occurred in low densities in the mid to upper
canopy layers. The upland understory was composed of a mixture of regenerating
saplings of the hardwood overstory, and hobblebush (Viburnum alterniflora),
striped maple (Acer spicatum), beaked hazelnut (Corylus cornuta), and mountain
27
maple (Acer pennsylvanicum). My work focused upon avian use of yellow birch,
sugar maple, American beech, and balsam fir because these trees account for 9297% of the trees on the study grids.
This study landscape was shared by several other research projects from the
Universities of New Brunswick and Universite dé Moncton in conjunction with the
Sustainable Forest Management Network of Centres of Excellence (NCESFM) and
Natural Sciences and Engineering Research Council of Canada (NSERC). Various
projects included landscape influences on mammal population structure (Bowman 2000
Bowman et al. 2000, Bowman et al. 2001), and avian productivity (Gunn 2002, Gunn et
al. 2000, Bourque and Villard 2001).
We employed systematic sampling after the methods of Fortin et al. (1989) and
Roland and Taylor (1997). Systematic sampling provides statistical properties
comparable to random sampling (McPherson 1990, Hayak and Buzas 1997, Bart et al.
1998), but avoids a priori imposition of perceived patterns upon the landscape. Wiens
(1989) cites the work of Taylor et al. (1984), who employed both a stratified random
sampling and systematic sampling design. They found that systematic sampling is better
suited for investigation of floristic composition effects. Wiens (1989) argues that
previous studies documenting the significance of vegetation structure over floristics
might have been biased by reliance upon stratified random sampling considering the
results of Taylor et al. (1984).
We established a 64 point grid system on the two separate 4900 ha landscapes
(Figure 2.2). Points were 1 kilometre apart on these macro-grids. Within each of these
two landscapes, two smaller 64 point grid systems were established. Points were 250
28
meters apart on these meso-grids. My work was conducted on the four meso-grids within
the two macro-grids. One meso-grid in each macro-grid was composed of mature, closed
canopy, upland forest dominated by hardwood. The other meso-grid in each landscape
differed in that the stands had been selectively harvested within the past 15 years. The
habitat requirements of the focal bird species precluded use of other cover types such as
regenerating clearcuts and plantations.
29
Grid Vegetation Sampling
We sampled vegetation at each grid point using a modification of the methods
employed by Hagan et al. (1996). We established three separate belt transects that
radiated from each grid point (Figure 2.3). We used these to sample all woody and
herbaceous plants and a variety of physical parameters. The length and width of the belt
varied according to the parameters being measured. I used only the tree data in the
analyses for this work as my primary interest was in differential use of tree species as a
foraging substrate. While understory vegetation might have an influence on tree species
use through a community pathway, I designed this study to examine avian predator,
arthropod prey, and tree species substrate interactions first.
Tree transects were 10 x 20 meters. All trees greater than or equal to 8 cm
diameter at breast height (dbh) and located within the belt transect were identified to
species and their dbh recorded. The density and dbh allowed calculations of basal areas
for each species of tree at each grid point and for the entire grid. These measurements
were necessary for calculation of availability of tree species to foraging songbirds.
30
Foraging Behaviour
There has been confusion over the concepts of resource use, selection and
preference, so it is worthwhile to outline here how these terms are interpreted and
applied. I tested for selective use in this study, as have most field observational studies in
spite of their claim to have documented resource preference. Preference is better
determined in a strictly experimental setting where resources are equally available
(Litvaitis et al. 1996).
Bart et al. (1998) presented a slightly different interpretation of preference. They
claim the proportions of available resources may vary and that preference is demonstrated
if the use of the resources remains unchanged in spite of varying availability. This
definition is closer to the concept of selective use that most investigators have employed
in field-based studies. If a resource is used out of proportion to its availability to an
animal, then that use is said to be selective (Johnson 1980). If a resource is used in
proportion to its availability then the use is indiscriminate or random. The distinction
made by Bart et al. (1998) is that in order to claim a resource is preferred, use of it must
remain consistent in spite of adjustments to its availability, whereas Litvaitis maintains
that preference is demonstrated only if resources remain equally available.
My design, as with most field-based work, cannot adjust resource proportions
temporally, nor does it provide for equal proportions. I elected to study resource use in
terms of selective use, selective avoidance, or random use, and simply avoid the concept
of preference.
Robinson and Holmes (1984) measured number of attacks on prey per minute for
4 species of forest songbird, including two of the species I studied, black-throated blue
31
warbler, and American redstart.
I have computed two different foraging rates, attacks
per unit time and attacks per forage flight. Attacks per unit time is the same as the rate
calculated by Robinson and Holmes (1984). Both of our rate variables are measures of
efficiency, one in terms of temporal units, the other in terms of spatial units. Attacks per
forage flight is the prey yield in a given unit of branch and or volume of foliage searched
by the bird before flying to the next region of branch, or to a completely different branch.
Robinson and Holmes (1982) report that this search area, which I will call a foliage
volume, has a radius up to 1 meter.
I conducted observations on black-throated blue warbler, black-throated green
warbler, American redstart, and least flycatcher (Empidonax minimus), found within a
100 meter radius of the meso-grid points. I used all-occurrences sampling in conjunction
with focal-animal sampling (Lehner 1996) to collect a specific set of observations on
individuals of the focal species. All-occurrences sampling is alternatively known as
event sampling (Hutt and Hutt 1970) and complete-record sampling (Slater 1978). I
selected a set of specific behaviours related to foraging and display. Under alloccurrences sampling every occurrence of these behaviours is recorded along with a
record of elapsed time. The period of time a bird was under continuous observation in
an individual tree is defined here as an observation sequence. I located focal birds
usually through their territorial song prior to first visual contact. In this manner, there is
not likely any bias toward any particular manoeuvre being associated with a tree species.
My analyses are confined to observations collected on males only. In general, more
effort was devoted to observation of black-throated blue and black-throated green
warblers and this is reflected in the sample sizes obtained.
32
Remsen and Robinson (1990) present a five part model of foraging behaviour
that includes search movements, attack movements at prey or substrate containing prey,
foraging site, food items, and food handling. I focused efforts on the first three, finding
the latter two observations occurring too infrequently for analysis. It is well established
that though forage attacks might not necessarily be successful, they are not initiated
unless prey is detected (Holmes and Robinson 1981, Remsen and Robinson 1990,
Lovette and Holmes 1995). While foraging manoeuvres such as hops and flights do not
necessarily indicate the presence of prey, attacks do.
My use and interpretation of the various foraging variables is similar to that
employed by Holmes and Robinson (1981). Recorded behaviours included the foraging
manoeuvre (e.g. glean, hover, hawk, hover-glean), frequency of hops on a branch,
frequency of flights, and duration of the observation sequence. Location of behaviour
was also recorded, including tree species, size of tree, zone of tree, and tree condition.
The behaviours I recorded included the attack manoeuvre (e.g. glean, hover, hawk,
hover-glean), foraging manoeuvre (e.g. frequency of hops and flights), and duration of
the observation sequence. our, including tree species, size of tree, and vertical zone of
the forest.
Hops are leg-propelled movements along the tree branch or twig in search of prey
items and flights are usually short rapid flights along a branch or to a new branch within
the same tree followed by another sequence of hopping. I defined glean, hover, and
hover-glean respectively as attacks directed toward prey on a leaf from a perched
position, attacks directed toward prey on a leaf while hovering underneath, and attacks
33
directed at foliage from above while in flight. The hawk is an attack manoeuvre directed
at prey in the air column rather than on leaves.
I recorded the tree species and vertical zone of the forest for all behavioural
observations. The focal species forage primarily in two vertical zones in the forest.
Black-throated green warbler concentrates its activity in the middle to upper strata
(Morse 1993), while black-throated blue warbler concentrates in the lower to middlestrata (Robinson and Holmes 1984). Male black-throated blue warblers foraged at a
height of 5.9 +/- 3.8 SD m (Holmes 1994). American redstarts forage from the ground to
the top of the canopy, with foraging heights for males averaging 10.9 m +/- SD (Sherry
and Holmes 1997). Sherry (1979) reported that least flycatchers foraged in the upper
canopy at heights averaging 12-15 m.
Calculation of tree species use was based on number of attacks on potential prey
items in relation to the availability of a tree species (Holmes and Robinson 1981). This
calculation is derived from the generally accepted method of calculating use of a resource
in proportion to its availability (Litvaitis et al. 1996, Bart et al. 1998). The resource here
is the leaf area of each tree species determined on a relative basis from the basal areas
(Holmes and Robinson 1981, Dodge et al. 1990) of American beech, yellow birch, sugar
maple and balsam fir. Two different measures of foraging rate were calculated. Both
variables use the number of attack manoeuvres. For one variable the number of attacks is
related to units of time, and for the other the number of attacks is related to the number of
flights. The former is reported as the attacks per minute and the latter as attacks per
flight. Attacks per flight is a spatial variable as attacks are conducted in a defined area
34
(e.g. along a branch) bounded by a flight to that section of branch and away from that
section of branch.
My use and interpretation of the various foraging variables is similar to that
employed by Holmes and Robinson (1981). The behaviours I recorded included the
attack manoeuvre (i.e. glean, hover, and hawk). I defined glean and hover respectively as
attacks directed toward prey on a leaf from a perched position and attacks directed toward
prey on a leaf while hovering underneath. The hawk is an attack manoeuvre directed at
prey in the air column rather than on leaves.
35
Diet Composition
I required avian diet data from focal bird species to confirm that arthropod
samples from the trees included the prey items consumed by the birds observed foraging.
It is conceivable that an arthropod sampling technique might not capture crucial
components of a bird’s diet. This would render conclusions about foraging site selection
based upon arthropod community data questionable. This component of my work was
designed to ensure that the arthropods sampled from the arboreal community included
those arthropods consumed by the focal bird species. Rosenberg and Cooper (1990)
comment that most studies on avian foraging ecology overlook this important logical
connection between foraging behaviour and the prey items collected from the substrate.
(For a review of collection means see Diamond and McKinley appendix 1).
Rosenberg and Cooper (1990) cite three methods to quantify diet items. (1)
Percent occurrence is a measure of the presence of a prey item without any statement
about abundance. It is useful in partially digested samples containing a mix of arthropod
body parts. (2) Frequency requires a count of individual prey items in their entirety, not
practical in a digested sample. (3) Percent volume and percent weight estimates require
identification of all body parts without assigning them to a specific number of prey items.
This method is not practical in stomach samples containing hundreds of exoskeletal parts.
I selected the first method of prey item quantification, and calculated percent occurrence
of each arthropod order across all stomach samples for each bird species separately. I
recorded the presence of an arthropod, either through the presence of an intact individual
or the presence of at least one distinctive body part indicative of a particular order. This
measure was essentially one of presence or absence of an order in the sample obtained
36
from each individual bird. The percent tally shows the proportion of individuals by bird
species that had a particular arthropod order in its stomach sample.
I captured black-throated blue warblers and black-throated green warblers on the
mm-grid and im-grid during the 1998 and 1999 breeding seasons. Territorial males were
lured into mist nets using playback of male song in conjunction with model birds placed
near the mist net. I used syrup of ipecac to induce emesis (Diamond and McKinley,
Appendix 1) in the captured birds.
37
Arthropod and Tree Species Associations
I designed this component of my study to test the arthropod hypothesis.
Ornithologists have addressed the question of arthropod availability to birds by a
variety of methods (Wolda 1990). As with sampling other taxonomic groups one may
wish to derive an estimate of relative abundance (index), or an estimate of absolute
abundance (density). Methods used to obtain an index include the use of sticky traps,
malaise traps, shake-cloth methods, sweep-net sampling, and pitfall traps. Methods used
to estimate density include collection of vegetation, stationary suction traps, portable
vacuum sampling, and counts of individuals from direct observation (Cooper and
Whitmore 1990).
I equipped a pole pruner with a cloth basket to clip and retrieve foliage samples
(Majer et al. 1990) from American beech, sugar maple, yellow birch, and balsam fir. I
mounted a bag 1 meter deep and 0.5 meters in diameter was mounted on a stiff wire
frame which was mounted on the cutting head of a set of pole pruners.
I slipped the
pole pruning bag over each foliage sample slowly to minimize disturbance of arthropods
present. Foliage, branches and twigs were not distorted to fit the bag, and movement of
the bag over the end of the branch was stopped when the branch reached the bottom. I
clipped the branch and lowered the bag immediately to search foliage, branches and bag
for arthropods. I placed the arthropods in 70% solutions of ethanol, and sealed the
foliage samples in plastic bags for storage at 4C. I later searched the foliage samples for
additional arthropods while counting leaf numbers.
38
I collected foliage samples at grid points on the mm-grid in 1998 and at points on
the mm-grid and im-grid in 1999. I developed a sampling scheme to provide an estimate
of arthropod density and diversity per unit of tree foliage area from the two primary
vertical feeding zones used by the focal birds. These zones were located at 3 meters
(zone 1) and 12 meters (zone 2) above the ground. These zones are based upon the
previously described foraging strata for the focal bird species. I cut foliage samples from
zone 1 from the nearest representative of each tree species >4cm dbh that possessed
foliage within reach of the pole pruner cutting head and basket. I cut foliage samples
from zone 2 from the nearest representative of each tree species >8cm dbh that possessed
foliage within reach of the pole pruner cutting head and basket. The tree selection criteria
were further constrained by selecting trees of similar height within each zone across all
points sampled so that age of foliage was controlled. The region sampled from trees of
both zones was the middle to upper middle portion of the tree.
I calculated arthropod densities per unit area of leaf and per clip sample. I used a
polar planimeter to calculate average areas for the leaves of each tree species and counted
the number of leaves in each sample to yield a density of arthropods per unit area of leaf.
The number of arthropods per clip sample is simply the count obtained for each order for
a given clipping in a tree species in a given zone. As the densities from zones 1 and 2 did
not differ (anova p<0.05), no distinction between them was made in subsequent analyses.
39
Landscape Distribution and Productivity
If there is a relationship between the abundance of a tree species and either the
presence or productivity of a bird species, that relationship should be strongest between
black-throated green warblers and American beech. I predict a similar relationship
between black-throated blue warbler and American beech. These predictions are based
upon the results from the selective foraging component of this study that demonstrated
higher foraging success for these bird species in American beech. American redstart may
also exhibit this relationship, but it is more likely for the two Dendroica warblers because
these species foraged in American beech more often. The lack of an association between
the abundance of a tree species and either the presence of that species or the productivity
of that species does not necessarily imply that the tree species is not important. It could
mean that a minimum threshold density for a particular tree species has been reached. I
also predict that species recorded during the point counts that possess foraging strategies
similar to the Dendroica warblers will be more likely to demonstrate an association
between their presence at a point and American beech abundance.
Predictions concerning tree species distribution in relation to avian distribution
and productivity stem from my foraging ecology work discussed earlier in this thesis.
The predictor variable I selected was the basal area of American beech, yellow birch, and
sugar maple, the three dominant hardwood tree species. I used logistic regression to
examine the relationships among these variables and the presence of foliage gleaning
birds (including my focal species) in the independent avian landscape census.
40
We used point counts to conduct the independent avian census in the reference
landscape during the 1996 and 1997 field seasons (NCESFM, New Brunswick,
unpublished data). All species within 100 meters of a point were recorded within a five
minute period during two separate visits within each season (Blondel et al. 1981,
Morrison et al. 1981, Bibby et al. 1993, Hagan et al. 1996, and Hagan et al. 1997).
I used the point count data to determine the presence or absence of a bird species
at a grid point. I elected to use presence/absence data rather than an estimate of
abundance since many of these species were registered only once or twice during a single
point count. A bird recorded at least once at a point on either round or in either year of
the point count data collection counted as a registration. Multiple registrations within a
round or over both rounds were not given extra weight, a species was either present or
absent at a point for the breeding season. I determined presence and absence of the four
focal bird species, American redstart, black-throated blue warbler, black-throated green
warbler, and least flycatcher at each grid point. I also determined presence and absence
of the following species: northern parula Parula americana, red-eyed vireo Vireo
olivaceus , blue-headed vireo Vireo solitarius, Philadelphia vireo Vireo philadelphicus,
yellow-rumped warbler Dendroica coronata, magnolia warbler Dendroica magnolia,
chestnut-sided warbler Dendroica pensylvanica, and scarlet tanager Piranga olivacea. I
selected these species because they forage from tree foliage and might exhibit patterns of
presence and absence with respect to tree species similar to the focal species.
41
I used results from a colleague’s study (Gunn 2002) conducted on the same study
plots during the same field seasons to examine avian productivity across the landscape in
terms of stand composition. His analyses included three of my focal species and several
additional foliage foraging species.
42
Table 2.1. Relative proportions of the four focal tree species on each grid.
Tree Species
American beech
balsam fir
sugar maple
yellow birch
mmgrid
0.41
0.1
0.37
0.13
43
im-grid
0.02
0.23
0.40
0.34
Figure 2.1. New Brunswick study site location.
44
Figure 2.2. Schematic diagram of research grid design.
45
Figure 2.3. Schematic diagram of vegetation sampling plots.
46
Chapter 3 Foraging Results
Foraging Behaviour Results Overview
Table 2.1 presents the number of observation sequences and the mean duration in
seconds of each observation sequence by bird species, year, and research grid.
Observations in the im-grid were limited to the years reported, 1997 and 1999. There are
no data reported on the im-grid in 1999 for the American redstart as reduced collection
efforts for this species yielded only three observation sequences. The number of
observation sequences for least flycatcher and American redstart in the latter two years of
the study reflect the lower effort devoted to observation of these two species.
Conversely, there are more observation sequences for black-throated blue and blackthroated green warblers as I directed more effort toward collecting data on these species.
Following the concerns of Hejl et al.(1990) and Bell et al. (1990) I examined the
data for autocorrelation prior to applying the chi-square goodness of fit tests to the
sequential observations. I found an insignificant degree of autocorrelation at a maximum
temporal lag of two observation sequences. The concern in applying chi-square tests to
such data is that the standard errors will be underestimated. I resampled the data using
the jackknife procedure to estimate the standard errors free of any degree of
autocorrelation. The standard error (SE = 0.0114) was the same value in the original data
set and the jackknifed data set. I concluded that chi-square goodness of fit tests could be
applied to the sequential data.
Table 2.2 reports the sum of foraging attacks made by each bird species in each
tree species for the four years of this study. As mentioned previously, there were only
47
two years (1997 and 1999) of data collected on the intensively managed grids. During
years 1996 and 1997 I used 3 person field crews and 2 person field crews for the years
1998 and 1999. Consequently, there were more observation sequences (Table 2.1) and
higher attack numbers (Table 2.2) recorded overall in 1996 when the intensively
managed grid was not under study and a 3 person field crew was at work. In 1997 the
efforts of the three person field crew were divided over two grids (managed and
reference) and this is reflected in the lower numbers of observation sequences and total
attack numbers. In 1998 I used a two person field crew, but did not work on the
intensively managed grid. The low numbers of observation sequences and attack
numbers for 1999 reflect the two person field crew now covering managed and
moderately managed grids. The standard errors for these various years and bird species
remain comparable.
Foraging Site Selection
It is commonly considered that expected values in a chi-square goodness of fit test
must be at least 5.0 (Zar 1996). There were only three combinations of bird species/year/
/grid where there were expected values below 5 where there were also significant
differences in expected versus observed tree species usage. These three cases were:
American redstart/mm-grid/1997, least flycatcher/mm-grid/1997, and least
flycatcher/mm-grid/1998 (see Tables 1.1 and 2.2).
Data were available for 23 of the 24 combinations of bird species/year/grid (Table
2.2). Twenty cases out of 23 showed a significant result (p<0.05) for use of all four tree
species versus their availability (Table 2.3). The results in 14 of these cases were
48
significant at p< 0.001 (Table 2.3) . Thus it is apparent that tree species differed in the
foraging opportunities they offered to birds.
After determining that use of the tree species was not random in terms of overall
attacks versus availability of all tree species, I tested the statistical significance of the
proportional use versus availability of each pairwise comparison of tree species. I
constructed confidence intervals with the alpha level adjusted for multiple simultaneous
comparisons (Litvaitis et al. 1996). The dominant trend in the mm-grid for all four bird
species in all four years (Figures 2.1-2.6) is selective use of beech and selective
avoidance or use in proportion to availability of yellow birch, sugar maple, and balsam fir
(p<0.05).
It was selectively avoided in one case, (American redstart in 1999), and used in
proportion to its abundance in the remaining 4 cases. In only one year and for one bird,
(American redstart in 1999), was birch selected out of proportion to its abundance. In 9
of the cases, birch was selectively avoided, and in the remaining 6 cases use was in
proportion to availability. Sugar maple was selectively used in only one year by one
species of bird, the least flycatcher in 1999. In 8 cases it was avoided and in the
remaining 7 cases, use was in proportion to availability. Fir was selectively used in one
case, (black-throated green warbler in 1999), selectively avoided in 10 cases, and used in
proportion to its abundance in the remaining 4 cases.
Birch, maple and fir were selectively used in only 1 of 16 cases each while beech
was selectively used in 11 cases. Beech was selectively avoided in only one case while
birch, maple and fir were avoided in 9, 8, and 10 cases respectively. The selection of
49
beech is one striking result. Another striking pattern here is the consist avoidance of the
other three species.
Figures are presented only for those years and bird species where some significant
difference in use was found. Review of Figures 2.1- 2.6 show similar patterns of use and
availability for the four tree species for black-throated blue warbler, least flycatcher, and
American redstart for years 1996 through 1998. In year 1999 these three bird species
show a relatively lower use of the beech and either higher use of the sugar maple as with
the flycatcher and black-throated blue warbler, or higher use of the birch as with the
American redstart. The years 1996, 1997, and 1999 for black-throated green warbler
show similar patterns of selective use and avoidance as those shown by the other three
species of bird. The departure from the trend for the black-throated green warbler occurs
in 1998.
50
Forage Rate
The foraging rate data measured both in terms of time and number of flights were
not normally distributed. Consequently, I applied the nonparametric Kruskal-Wallis test
to evaluate the differences in the two foraging rate variables among the four tree species.
I used two different post-hoc tests to determine the significance of multiple pairwise
comparisons of both foraging rate variables for each tree species. I used the
nonparametric post-hoc Nemenyi test (Zar 1996) and multiple Mann-Whitney tests
(Sheskin 1997). The Nemenyi test adjusts alpha for the multiple comparisons. These
results are reported in Table 2.4. As it was my original intent to test the foraging rates
among tree species a priori, I concur with Sheskin that use of the Mann-Whitney test is
justified as long as the specific comparisons made were formulated a priori. These
results are reported in tables 2.5-2.8. In both cases, only those combinations of year and
bird that yielded significant results are reported.
The more conservative approach of the Nemenyi post-hoc test shows significant
results (p<0.05) for one bird species in one year, the black-throated green warbler in
1996, for attacks per unit time only. Three pairwise comparisons are significantly
different in this test including higher foraging rates in beech and maple and lower rates in
fir and birch. Multiple Mann-Whitney tests reveal a similar pattern, but in several more
cases as this post-hoc approach is less conservative than the Nemenyi which adjusts the
alpha level. Foraging rates did not differ among tree species on the intensively managed
grid. As beech was the tree associated with higher foraging rates on the moderately
managed grid, yet in only a limited number of cases, perhaps it is not surprising that the
51
intensively managed grid, lacking the beech component, showed no foraging rate
variation among tree species.
Foraging rates measured as attacks per unit time are different (p<0.05) in 1996
and 1999 for black-throated blue and black-throated green warblers respectively (Tables
2.4-2.5) as determined by multiple Mann-Whitney post-hoc tests. Foraging rate
measured as attacks per flight are different (p<0.05) in 1996 and 1999 for black-throated
green warbler only (Tables 2.6-2.7) as determined by multiple Mann-Whitney post-hoc
tests. The post-hoc Nemenyi test shows a difference for one bird species, black-throated
green warbler in only one year, 1996. The dominant trend revealed by either post-hoc
test is for higher foraging rates in beech over any other species of tree.
52
Forage Manoeuvre Results
Table 3.1 reports attack manoeuvres by bird and tree species, these are the
observed values used for the chi-square tests. American redstart, least flycatcher, blackthroated blue warbler and black-throated green warbler total forage attacks in the four
focal tree species combined were 77, 240, 177, and 147 respectively (Table 3.1).
Expected values were derived from the proportion of a particular forage manoeuvre
expected to occur in a tree species based upon that tree species abundance in the
landscape if forage manoeuvres were being conducted randomly with respect to tree
species abundance. All birds showed a significant difference (chi-square p < 0.05) in
their use of the hover among tree species (Table 3.2). The only species to show a
significant difference (chi-square p <0.05) in the use of the hawk was least flycatcher
(Table 3.2). Two species, black-throated green warbler and American redstart, exhibited
a significant difference (chi-square p < 0.05) in their use of the glean manoeuvre (Table
4.2).
Post-hoc multiple comparisons were made after adjustment of alpha levels so that
I might draw inferences central to the hypothesis concerning the use of the hover
manoeuvre in relation to beech and birch leaf and branch morphology. These results are
reported in Figures 3.1-3.4.
53
The black-throated blue warbler and American redstart hovered in higher
proportions in American beech (Figures 3.2 and 3.3 respectively, chi-square
p<0.05,). Hovers by black-throated green warbler in American beech were not
significantly different (Figure 3.2, p>0.05). Proportions of hovers performed by
black-throated green warbler and American redstart in yellow birch were
significantly lower (Figures 3.1 and 3.3 respectively, chi-square p<0.05) than in
other tree species. Proportion of hovers by the black-throated blue warbler in
yellow birch were not significantly different (Figure 3.2, chi-square p>0.05).
Neither black-throated blue (Table 3.2, chi-square p<0.05,) nor blackthroated green warbler (Figure 4.2, chi-square p<0.05) performed higher
proportions of gleans in the broad leaved trees; American beech, yellow birch,
and sugar maple. American redstart performed a higher proportion of gleans in
beech (Figure 3.3, chi-square p < 0.05). Black-throated green warbler did show a
higher proportion of gleans in balsam fir (Figure 3.1, chi-square p<0.05).
Diet Composition
Representatives of 9 arthropod orders were recovered from the stomach samples
of the two bird species. The nine arthropod orders occurred in statistically similar (chisquare p>0.05) proportions in the samples obtained from both Dendroica species.
Members of the order Araneida (spiders) were present in more samples than any other
order and in similar proportions for both bird species. Exoskeletal remains of several
arthropod orders were recovered from all samples. Orders identified included araneida,
trichoptera, coleoptera, diptera, hemiptera, lepidoptera, thysanoptera, homoptera, and
hymenoptera.
54
The orders most frequently encountered in the samples from both warbler species
were Araneida, Coleoptera, Diptera, and Hymenoptera. Araneida was found in > 75% of
the samples for both warblers, and Coleoptera was in > 60 % of the samples for both
birds. Diptera was in > 20 % of black-throated green warblers and > 60 % of blackthroated blue warblers. Hymenoptera was in >50% of black-throated green warblers and
>30% of black-throated blue warblers (Figure 3.21). There were no significant
differences (chi-square p>0.05) between the Dendroica species in the proportional
occurrence of an arthropod order based upon the following two assumptions: 1) no orders
are missed due digestion of a diagnostic body part, and 2) the sample collected included
all stomach contents.
55
Table 3.1. Number of observation sequences by grid, bird species, and year with mean
duration of sequence and standard error (SE).
Bird
Year
Grid*
N Sequences
amre
amre
amre
amre
lefl
lefl
lefl
lefl
btbw
btbw
btbw
btbw
btgw
btgw
btgw
btgw
amre
lefl
lefl
btbw
btbw
btgw
btgw
1996
1997
1998
1999
1996
1997
1998
1999
1996
1997
1998
1999
1996
1997
1998
1999
1997
1997
1999
1997
1999
1997
1999
mm
mm
mm
mm
mm
mm
mm
mm
mm
mm
mm
mm
mm
mm
mm
mm
im
im
im
im
im
im
im
136
383
264
14
377
67
131
34
675
261
452
201
223
238
360
134
28
27
38
118
172
302
83
*
mm signifies moderately managed grid, im signifies intensively managed grid
56
Mean Duration
secs.
19.8
28.1
11.6
25.7
37.0
32.0
24.9
30.6
33.2
34.3
18.4
25.8
69.2
27.2
17.1
20.9
35.7
28.0
25.0
26.0
13.0
17.0
27.0
SE
1.2
2.6
1.1
6.1
2.8
8.8
4.4
6.9
2.4
3.2
1.5
3.7
10.7
2.0
1.1
5.5
8.0
6.0
8.8
4.4
1.1
1.9
4.0
Table 3.2. Number of attacks each season by bird and tree species, and mean number of
attacks per observation sequence with standard error SE by grid and year.
ambe
bafi
suma
yebi
N
55
3
20
4
amre
Mean
0.57
0.38
0.57
1
SE
0.1
0.26
0.14
0.58
ambe
bafi
suma
yebi
134
6
26
15
0.62
0.86
0.42
0.38
0.07
0.71
0.1
0.1
ambe
bafi
suma
yebi
31
0
17
2
0.25
0
0.38
0.29
0.04
0
0.12
0.18
ambe
bafi
suma
yebi
0
0
0
8
0
0
0
0.89
0
0
0
0.42
ambe
bafi
suma
yebi
4
7
12
5
0.75
0.86
1.42
0.8
0.48
0.55
0.40
0.58
ambe
bafi
suma
yebi
na*
na
na
na
na
na
na
na
na
na
na
na
moderately managed grid 1996
lefl
btbw
N
Mean SE
N
Mean
161 0.3
0.05
280 0.57
26
0.46
0.09
14
0.58
0
0
0
56
0.36
0
0
0
15
0.52
moderately managed grid 1997
22
0.46
0.12
92
0.71
0
0
0
33
0.89
8
0.73
0.38
50
0.63
0
0
0
26
1.1
moderately managed grid 1998
13
0.19
0.06
65
0.28
0
0
0
15
0.31
1
0.09
0.09
35
0.25
1
0.33
0.33
16
0.55
moderately managed grid 1999
3
0.12
0.14
29
0.4
0
0
0
4
0.22
8
1
0.4
39
0.40
0
0
0
5
0.39
intensively managed grid 1997
0
0
0
0
0
0
0
0
0
0
8
0.33
0.16
35
0.52
0
0
0
38
0.76
intensively managed grid 1999
0
0
0
0
0
0
0
0
0
0
12
0.39
0.12
34
0.24
0
0.6
0.25
11
0.37
*
not available
57
SE
0.04
0.16
0.06
0.13
N
113
19
52
0
btgw
Mean
0.62
0.38
0.78
0
SE
0.07
0.1
0.1
0
0.1
0.46
0.13
0.35
89
19
28
21
0.79
0.7
0.42
0.72
0.11
0.21
0.16
0.22
0.05
0.1
0.05
0.19
38
24
32
12
0.27
0.41
0.25
0.34
0.05
0.11
0.05
0.16
0.09
0.22
0.08
0.18
27
3
9
1
0.49
0.18
0.18
0.08
0.14
0.01
0.07
0.08
0
0
0.1
0.15
2
18
134
32
0.33
1
0.57
0.74
0.21
0.38
0.09
0.15
0
0
0.04
0.11
1
10
29
12
0.5
1.7
0.51
0.67
0.05
0.16
0.16
0.24
Table 3.3. Goodness of fit analysis for foraging use versus availability of the four focal
tree species combined, chi-square p<0.05*, P<0.01**, P<0.001***, ns if not significant.
Bird species
amre
amre
amre
amre
lefl
lefl
lefl
lefl
btbw
btbw
btbw
btbw
btgw
btgw
btgw
btgw
amre
lefl
lefl
btbw
btbw
btgw
btgw
a
grida
mm
mm
mm
mm
mm
mm
mm
mm
mm
mm
mm
mm
mm
mm
mm
mm
im
im
im
im
im
im
im
Year
1996
1997
1998
1999
1996
1997
1998
1999
1996
1997
1998
1999
1996
1997
1998
1999
1997
1997
1999
1997
1999
1997
1999
mm signifies moderately managed grid, im signifies intensively managed grid.
58
P
***
***
**
***
***
**
*
ns
***
***
***
*
***
***
***
***
ns
**
*
***
***
***
ns
Table 3.4. Multiple comparison of btgw forage attacks per minute (Nemenyi test p<0.05)
for differences among tree species, 1996 moderately managed grid.
ambe
bafi
suma
yebi
ambe
ns*
ns
(ambe>yebi)
bafi
(suma>bafi)
ns
suma
(suma>yebi)
yebi
-
*
p values from Kruskal-Wallis tests are denoted as ns if not significant.
Table 3.5. Multiple comparison of btgw forage attacks per minute (Mann-Whitney p <
0.05) for differences among tree species, 1999 moderately managed grid.
ambe
bafi
suma
yebi
ambe
(ambe>bafi)
(ambe>suma)
(ambe>yebi)
bafi
ns*
ns
suma
ns
*
p values from Kruskal-Wallis tests are denoted as ns if not significant.
59
yebi
-
Table 3.6. Multiple comparison of btbw forage attacks per minute (Mann-Whitney test
p<0.05) for differences among tree species, 1996 moderately managed grid.
ambe
bafi
suma
yebi
ambe
ns*
(ambe>suma)
ns
bafi
ns
ns
suma
ns
yebi
-
*
p values from Kruskal-Wallis tests are denoted as ns if not significant.
Table 3.7. Multiple comparison of btgw forage attacks per flight (Mann-Whitney test
p<0.05) for differences among tree species, 1999 moderately managed grid.
ambe
bafi
suma
yebi
ambe
(ambe>bafi)
(ambe>suma)
(ambe>yebi)
bafi
ns*
ns
suma
ns
yebi
-
*
p values from Kruskal-Wallis tests are denoted as ns if not significant.
Table 3.8. Multiple comparison of btgw forage attacks per flight (Mann-Whitney test
p<0.05) for differences among tree species, 1996 moderately managed grid.
ambe
bafi
suma
yebi
ambe
(ambe>bafi)
(ambe>suma)
ns*
bafi
(bafi>suma)
ns
*
suma
(suma>yebi)
p values from Kruskal-Wallis tests are denoted as ns if not significant.
60
yebi
-
Table 3.9. Number of attack manoeuvres by tree species and bird species, all years
combined, moderately managed grid only.
ambe
bafi
suma
yebi
gln1
12
2
0
0
Amre
hwk2
8
5
0
2
hov3
31
12
1
4
gln
11
5
1
0
Lefl
hwk
66
18
0
0
hov
119
20
0
0
gln
34
17
8
9
Btbw
hwk
4
3
5
2
hov
67
14
6
8
gln
28
20
5
16
1
glean 2hawk 3hover
Table 3.10. Goodness of fit analysis for forage manoeuvres among tree species, chisquare p < 0.05.
Bird species
btbw
btgw
amre
lefl
Glean
ns
*
*
ns
Hawk
ns
ns
ns
*
* ns = not significant.
61
Hover
*
*
*
*
Btgw
hwk
8
2
0
2
hov
37
26
1
2
Least Flycatcher IM-Grid 1999
Proportions of Observed and Expected Forage Attacks
Attacks
Least Flycatcher IM-Grid 1997
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
obs.
exp.
ambe
bafi
suma*
yebi
obs.
exp.
ambe
Tree Species
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
suma
yebi
Black-throated Blue Warbler
IM-Grid 1999
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
obs.
exp.
bafi
suma*
Tree Species
Black-throated Blue Warbler
IM-Grid 1997
ambe
bafi
obs.
exp.
ambe
yebi*
bafi
suma*
yebi
Tree Species
Tree Species
Figure 3.1. Least Flycatcher and black-throated blue warbler observed foraging use and
expected foraging use based upon availability of each of the four focal tree species in the
intensively managed grid. Significant difference between use and availability (chi-square
p<0.05) after adjustment of alpha for multiple comparisons indicated by (*).
62
Proportions of Observed and
Expected Forage Attacks
Black-throated Green Warbler
IM-Grid 1997
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
obs.
exp.
ambe
bafi
suma*
yebi
Tree Species
Figure 3.2. Black-throated green warbler observed foraging use and expected foraging
use based upon availability of each of the four focal tree species in the intensively
managed grid. Significant difference between use and availability (chi-square p<0.05)
after adjustment of alpha for multiple comparisons indicated by (*).
63
Proportions of Observed and Expected Forage Attacks
American Redstart MM-Grid 1996
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
American Redstart MM-Grid 1997
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
obs.
exp.
ambe* bafi* suma* yebi*
yebi
Tree Species
American Redstart MM-Grid 1998
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
American Redstart MM-Grid 1999
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
obs.
exp.
suma
exp.
ambe* bafi* suma*
Tree Species
ambe* bafi*
obs.
yebi*
obs.
exp.
ambe* bafi* suma* yebi*
Tree Species
Tree Species
Figure 3.3. American redstart observed foraging use and expected foraging use based upon
availability of each of the four focal tree species in the moderately managed grid. Significant
difference between use and availability (chi-square p<0.05) after adjustment of alpha for
multiple comparisons indicated by (*).
64
Least Flycatcher MM-Grid 1997
Proportions of Observed and Expected Forage Attacks
Least Flycatcher MM-Grid 1996
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
obs.
exp.
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
suma yebi*
Tree Species
Tree Species
Least Flycatcher MM-Grid 1999
Least Flycatcher MM-Grid 1998
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
obs.
exp.
suma
exp.
ambe* bafi*
ambe* bafi* suma* yebi*
ambe* bafi*
obs.
yebi
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
obs.
exp.
ambe bafi* suma* yebi*
Tree Species
Tree Species
Figure 3.4. Least flycatcher observed foraging use and expected foraging use based
upon availability of each of the four focal tree species in the moderately managed grid.
Significant difference between use and availability (chi-square p<0.05) after adjustment
of alpha for multiple comparisons indicated by (*).
65
Proportions of Observed and Expected Forage Attacks
Black-throated Blue Warbler
MM-Grid 1996
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
Black-throated Blue Warbler
MM-Grid 1997
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
obs.
exp.
ambe*
bafi*
suma*
obs.
exp.
ambe
yebi*
bafi
suma*
yebi
Tree Species
Tree Species
Black-throated Blue Warbler
MM-Grid 1998
1
0.8
0.6
obs.
0.4
exp.
0.2
0
ambe*
bafi
suma* yebi*
Tree Species
Figure 3.5. Black-throated blue warbler observed foraging use and expected foraging
use based upon availability of each of the four focal tree species in the moderately
managed grid. Significant difference between use and availability (chi-square p<0.05)
after adjustment of alpha for multiple comparisons indicated by (*).
66
Black-throated Green Warbler
MM-Grid 1997
Proportions of Observed and Expected Forage Attacks
Black-throated Green Warbler
MM-Grid 1996
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
obs.
exp.
ambe*
bafi
suma
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
suma*
yebi
Black-throated Green Warbler
MM-Grid 1999
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
obs.
exp.
suma
bafi
Tree Species
Black-throated Green Warbler
MM-Grid 1998
bafi*
exp.
ambe*
yebi*
Tree Species
ambe
obs.
yebi
obs.
exp.
ambe* bafi*
Tree Species
suma
yebi*
Tree Species
Figure 3.6. Black-throated green warbler observed foraging use and expected foraging
use based upon availability of each of the four focal tree species in the moderately
managed grid. Significant difference between use and availability (chi-square p<0.05)
after adjustment of alpha for multiple comparisons indicated by (*).
67
Hover Manoeuvre
Number of Hovers
140
120
100
80
obs
60
exp
40
20
0
ambe
bafi*
suma
yebi*
Tree Species
Glean Manoeuvre
Number of Gleans
30
25
20
obs
15
exp
10
5
0
ambe
bafi*
suma
yebi
Tree Species
Figure 3.7. Forage manoeuvres performed in each tree species by black-throated green
warbler all years combined; *signifies a significant difference between hovers and
availability of the tree species (chi-square p<0.05) after adjustment of alpha for multiple
comparisons.
68
Hover Manoeuvre
Number of Hovers
140
120
100
80
obs
60
exp
40
20
0
ambe*
bafi
suma*
yebi
Tree Species
Figure 3.8. Forage manoeuvres performed in each tree species by black-throated blue
warbler all years combined; *signifies a significant difference between hovers and
availability of the tree species (chi-square p<0.05) after adjustment of alpha for multiple
comparisons.
69
Hover Manoeuvre
140
Number of Hovers
120
100
80
obs
60
exp
40
20
0
ambe*
bafi
suma
yebi*
Tree Species
Glean Manoeuvre
14
Number of Gleans
12
10
8
obs
6
exp
4
2
0
ambe*
bafi
suma
yebi
Tree Species
Figure 3.9. Forage manoeuvres performed in each tree species by American redstart all
years combined; *signifies a significant difference between hovers and availability of the
tree species (chi-square p<0.05) after adjustment of alpha for multiple comparisons.
70
Hover Manoeuvre
Number of Hovers
140
120
100
obs
80
exp
60
40
20
0
ambe*
bafi
suma*
yebi
Tree Species
Hawk Manoeuvre
Number of Hawks
70
60
50
40
obs
30
exp
20
10
0
ambe*
bafi
suma*
yebi
Tree Species
Figure 3.10. Forage manoeuvres performed in each tree species by least flycatcher all
years combined; *signifies a significant difference between hovers and availability of the
tree species (chi-square p<0.05) after adjustment of alpha for multiple comparisons.
71
Proportional Occurrence
0.35
0.3
0.25
0.2
btbw
0.15
btgw
0.1
0.05
ar
an
co
le
hy
m
e
di
pt
he
m
ho i
m
o
th
ys
tri
ch
le
pi
0
Arthropod Order
Figure 3.11. Proportional occurrence of arthropod orders in regurgitated stomach
samples, N=19 for black-throated blue warbler and N=25 for black-throated green
warbler.
72
Chapter 4 : Arthropod Prey Density and Diversity Results
I limited my analyses to the 4 most common arthropod orders in the stomach
samples (Figure 3.11), and lepidoptera. These four orders, araneida, coleoptera,
hymenoptera and diptera were the most common orders in the arboreal clip samples as
well. Other arthropod orders found in the stomach contents (Figure 3.11) occurred
infrequently.
Basic summary statistics from the densities calculated per unit of leaf area may be
found in Tables 3.1-3.4 for both grids over the two years that I gathered arthropod data.
As the im grid was not sampled in 1998, there are no results reported for this year. The
tables report the sum, mean, and standard error of the mean for the raw number of
arthropods from each taxonomic order collected in all clip samples from all species of
tree in each year. Table 1.1 reports the basal area of each tree species on the mm-grid
and im-grid. As this table indicates, American beech was almost absent from the im-grid.
73
I analyzed a subset of the arthropod orders collected from the trees. This subset
consisted of the five most common orders of arthropods found in the data pooled from
the stomach samples of black-throated green warbler and black-throated blue warbler.
Figures 3.1-3.20 show the results of those analyses of variance where a significant
(p<0.05) difference was detected among tree species for the arthropod parameters
calculated based upon density estimates corrected for units of leaf area and based upon
density estimates per clip sample. Based upon these analyses of variance it was far more
likely that a significant difference would be demonstrated using the arthropod densities
corrected for leaf area. Arthropod densities per clip sample were more likely to be
statistically similar.
Yellow birch usually had higher densities of all arthropod prey combined, higher
densities of many individual orders, and higher overall taxonomic richness (Tables 4.14.5). Table 4.4 reports the results of post-hoc Bonferonni tests of the multiple
comparisons made based upon total unit area of leaves sampled. Table 4.5 reports the
results of post-hoc Bonferonni tests of the multiple comparisons made based upon the
clip sample. The dominant pattern observed with both methods of calculating density
was a higher density of most arthropod orders in yellow birch. This pattern prevailed
regardless of year, period within season, vertical zone within a tree, and managed versus
moderately managed grid. Overall taxonomic richness was usually higher in yellow
birch as well.
74
Table 4.1. Total number, mean (per cm2), and standard error (SE) of occurrence of
arthropod orders for moderately managed grid 1998.
order
araneida
coleoptera
hymenoptera
diptera
lepidoptera
N
77
22
21
12
6
order
araneida
coleoptera
hymenoptera
diptera
lepidoptera
N
121
10
49
17
39
order
araneida
coleoptera
hymenoptera
diptera
lepidoptera
N
83
11
28
24
18
order
araneida
coleoptera
hymenoptera
diptera
lepidoptera
N
108
126
37
30
13
American Beech
mean
2
1.6
1.3
1
2
Balsam Fir
mean
2.1
1.1
1.7
1.31
3.54
Sugar Maple
mean
1.93
1
1.4
1.2
2
Yellow Birch
mean
2.20
2.93
1.76
1.58
1.44
75
standard error
0.23
0.29
0.15
0
0.56
standard error
0.2
0.11
0.22
0.13
1.76
standard error
0.17
0
0.2
0.09
1
standard error
0.24
0.40
0.30
0.28
0.34
Table 4.2. Number, mean (per cm2), and standard error (SE) of occurrence of arthropod
orders for moderately managed grid 1999.
order
araneida
coleoptera
hymenoptera
diptera
lepidoptera
N
12
9
16
10
5
order
araneida
coleoptera
hymenoptera
diptera
lepidoptera
N
22
13
27
7
4
order
araneida
coleoptera
hymenoptera
diptera
lepidoptera
N
20
7
13
6
6
order
araneida
coleoptera
hymenoptera
diptera
lepidoptera
N
10
116
4
10
3
American Beech
mean
0.38
0.28
0.50
0.31
0.16
Balsam Fir
mean
0.65
0.38
0.79
0.21
0.12
Sugar Maple
mean
0.63
0.22
0.41
0.19
0.19
Yellow Birch
mean
0.29
3.41
0.12
0.29
0.09
76
standard error
0.09
0.11
0.19
0.11
0.09
standard error
0.16
0.10
0.23
0.08
0.06
standard error
0.15
0.09
0.12
0.08
0.08
standard error
0.09
0.62
0.07
0.10
0.05
Table 4.3. Number, mean (per cm2), and standard error (SE) of occurrence of arthropod
orders for intensively managed grid 1999.
order
araneida
coleoptera
hymenoptera
diptera
lepidoptera
N
0
1
0
1
0
order
araneida
coleoptera
hymenoptera
diptera
lepidoptera
N
25
11
16
5
4
order
araneida
coleoptera
hymenoptera
diptera
lepidoptera
N
33
19
11
6
8
order
araneida
coleoptera
hymenoptera
diptera
lepidoptera
N
37
253
4
8
5
American Beech
mean
0
1
0
1
0
Balsam Fir
mean
0.81
0.36
0.52
0.16
0.13
Sugar Maple
mean
0.89
0.51
0.30
0.16
0.22
Yellow Birch
mean
0.97
6.66
0.11
0.21
0.13
77
standard error
na
na
na
na
na
standard error
0.14
0.12
0.13
0.07
0.06
standard error
0.17
0.14
0.10
0.06
0.09
standard error
0.51
1.10
0.05
0.07
0.06
Table 4.4. Significant (p<0.05) Bonferonni post-hoc pair-wise comparisons of arthropod
variables, data based on number per unit leaf area.
arthropod variable
grid
year
comparison
rich1
rich
rich
dens2
dens
dens
aran3
aran
aran
hyme4
hyme
cole5
cole
cole
dens
dens
cole
cole
dens
dens
dens
aran
aran
aran
cole
mm
mm
mm
mm
mm
mm
mm
mm
mm
mm
mm
mm
mm
mm
im
im
im
im
mm
mm
mm
mm
mm
mm
mm
1998
1998
1998
1998
1998
1998
1998
1998
1998
1998
1998
1998
1998
1998
1999
1999
1999
1999
1999
1999
1999
1999
1999
1999
1999
yebi>ambe
yebi>bafi
yebi>suma
yebi>ambe
yebi>bafi
yebi>suma
yebi>ambe
yebi>bafi
yebi>suma
yebi>ambe
yebi>suma
yebi>ambe
yebi>bafi
yebi>suma
yebi>suma
bafi>yebi
yebi>suma
yebi>bafi
yebi>ambe
suma>yebi
bafi>yebi
bafi>ambe
bafi>suma
bafi>yebi
yebi>bafi
1
order richness per unit area, 2density of all arthropods per unit area, 3density of Araneida
per unit area, 4density Hymenoptera per unit area, 5density of coleptera per unit area.
78
Table 4.5. Significant (p<0.05) Bonferonni post-hoc pair-wise comparisons of arthropod
variables, data based on total clip sample.
arthropod variable
grid
year
comparison
cole
rich1
dens2
dens
cole3
cole
dens
cole
dens
dens
dens
mm
mm
mm
mm
im
im
im
mm
mm
mm
mm
1998
1998
1998
1998
1999
1999
1999
1999
1999
1999
1999
yebi>suma
yebi>ambe
yebi>ambe
yebi>suma
yebi>suma
yebi>bafi
yebi>bafi
yebi>bafi
yebi>ambe
yebi>suma
yebi>bafi
1
order richness per clip sample, 2density all arthropods combined per clip sample,
density of Coleoptera per clip sample.
3
79
Table 4.6. Mean leaf number, mean leaf area, and standard errors by tree species.
Tree Species
ambe
suma
yebi
bafi*
Mean leaf
number per
clip sample
62
52
50
7500
SE leaf
number
Mean area
per leaf
(cm2)
5.1
6.1
6.8
1039
52
55
31
0.27
*
SE leaf
area
3.28
3.57
1.90
0.02
Mean leaf
area per
clip sample
cm2
3224
2860
1550
2025
A mean number of needles per cm of branchlet (se = 1.05) was used to calculate the
mean number of needles per clip sample.
80
Araneida Density per Clip R-Grid 1999
5
Araneida / Clip
4
3
2
1
0
ambe
bafi suma
Tree Species
yebi
Figure 4.1. Araneida density per branch and leaf clip sample by tree species. Moderately
managed grid 1999, anova p<0.05.
Coleoptera Density per Clip R-Grid 1999
5
Coleoptera / Clip
4
3
2
1
0
ambe
bafi suma
Tree Species
yebi
Figure 4.2. Coleoptera density per branch and leaf clip sample by tree species.
Moderately managed grid 1999, anova p<0.05.
81
Arthropod Density per Clip R-Grid 1999
5
Arthropods / Clip
4
3
2
1
0
ambe
bafi suma
Tree Species
yebi
Figure 4.3. Total arthropod density per branch and leaf clip sample by tree species.
Moderately managed grid 1999, anova p<0.05.
Araneida Density per square cm R-Grid 1999
Araneida / square cm
0.0010
0.0007
0.0003
0.0000
ambe
bafi suma
Tree Species
yebi
Figure 4.4. Araneida density per square centimetre of leaf area by tree species.
Moderately managed grid 1999, anova p<0.05.
82
Coleoptera Density per square cm R-Grid 1999
Coleoptera / square cm
0.0010
0.0007
0.0003
0.0000
ambe
bafi suma
Tree Species
yebi
Figure 4.5. Coleoptera density per square centimetre of leaf area by tree species.
Moderately managed grid 1999, anova p<0.05.
Arthropod Density per square cm R-Grid 1999
Arthropods / square cm
0.0010
0.0007
0.0003
0.0000
ambe
bafi suma
Tree Species
yebi
Figure 4.6. Total arthropod density per square centimetre of leaf area by tree species.
Moderately managed grid 1999, anova p<0.05.
83
Coleoptera Density per Clip M-Grid 1999
10
Coleoptera / Clip
8
6
4
2
0
ambe
bafi suma
Tree Species
yebi
Figure 4.7. Coleoptera density per branch and leaf clip sample by tree species.
Intensively managed grid 1999, anova p<0.05.
Arthropod Density per Clip M-Grid 1999
10
Arthorpods / Clip
8
6
4
2
0
ambe
bafi suma
Tree Species
yebi
Figure 4.8. Total arthropod density per branch and leaf clip sample by tree species.
Intensively managed grid 1999, anova p<0.05.
84
Coleoptera Density per square cm M-Grid 1999
Coleoptera / square cm
0.0010
0.0007
0.0003
0.0000
ambe
bafi suma
Tree Species
yebi
Figure 4.9. Coleoptera density per square centimetre of leaf area by tree species.
Intensively managed grid 1999, anova p<0.05.
Hymenoptera Density per square cm M-Grid 1999
Hymenoptera / square cm
0.0010
0.0007
0.0003
0.0000
ambe
bafi suma
Tree Species
yebi
Figure 4.10. Hymenoptera density per square centimetre of leaf area by tree species.
Intensively managed grid 1999, anova p<0.05.
85
Arthropod Density per square cm M-Grid 1999
Arthropods / square cm
0.0010
0.0007
0.0003
0.0000
ambe
bafi suma
Tree Species
yebi
Figure 4.11. Total arthropod density per square centimetre of leaf area by tree species.
Intensively managed grid 1999, anova p<0.05.
Coleoptera Density per Clip R-Grid 1998
10
Coleoptera / Clip
8
6
4
2
0
ambe
bafi suma
Tree Species
yebi
Figure 4.12. Coleoptera density per branch and leaf clip sample by tree species.
Moderately managed grid 1998, anova p<0.05.
86
Order Richness per Clip R-Grid 1998
Order Richness / Clip
10
8
6
4
2
0
ambe
bafi suma
Tree Species
yebi
Figure 4.13. Order richness per branch and leaf clip sample by tree species. Moderately
managed grid 1998, anova p<0.05.
Arthropod Density per Clip R-Grid 1998
10
Arthropods / Clip
8
6
4
2
0
ambe
bafi suma
Tree Species
yebi
Figure 4.14. Total arthropod density per branch and leaf clip sample by tree species.
Moderately managed grid 1998, anova p<0.05.
87
Araneida Density per square cm R-Grid 1998
Araneida / square cm
0.0050
0.0033
0.0017
0.0000
ambe
bafi suma
Tree Species
yebi
Figure 4.15. Araneida density per square centimetre of leaf area by tree species.
Moderately managed grid 1998, anova p<0.05.
Coleoptera Density per square cm R-Grid 1998
Coleoptera / square cm
0.0050
0.0033
0.0017
0.0000
ambe
bafi suma
Tree Species
yebi
Figure 4.16. Coleoptera density per square centimetre of leaf area by tree species.
Moderately managed grid 1998, anova p<0.05.
88
Hymenoptera Density per square cm R-Grid 1998
Hymenoptera / square cm
0.0050
0.0033
0.0017
0.0000
ambe
bafi suma
Tree Species
yebi
Figure 4.17. Hymenoptera density per square centimetre of leaf area by tree species.
Moderately managed grid 1998, anova p<0.05.
Diptera Density per square cm R-Grid 1998
Diptera / square cm
0.0050
0.0033
0.0017
0.0000
ambe
bafi suma
Tree Species
yebi
Figure 4.18. Diptera density per square centimetre of leaf area by tree species.
Moderately managed grid 1998, anova p<0.05.
89
Order Richness per square cm R-Grid 1998
Order Richness / square cm
0.0050
0.0033
0.0017
0.0000
ambe
bafi suma
Tree Species
yebi
Figure 4.19. Order richness per square centimetre of leaf area by tree species.
Moderately managed grid 1998, anova p<0.05.
Arthropod Density per square cm R-Grid 1998
Arthropods / square cm
0.0050
0.0033
0.0017
0.0000
ambe
bafi suma
Tree Species
yebi
Figure 4.20. Total arthropod density per square centimetre of leaf area by tree species.
Moderately managed grid 1998, anova p<0.05.
90
Chapter 5 Landscape Distribution and Productivity Results
Presence of three focal species was significantly and positively associated with
the basal area of a deciduous tree species in a logistic regression (p<0.05) (Table 1).
Black-throated green warbler presence was associated with basal area of American beech.
Black-throated blue warbler presence was associated with basal area of yellow birch.
American redstart presence was associated with basal area of sugar maple. Least
flycatcher showed no association between presence and the basal area of a tree species.
Two non-focal species, magnolia warbler and northern parula, demonstrated a significant
positive association between their presence and basal area of American beech (p<0.05,
Table 5.1).
Gunn (2002) measured reproductive success of some of these bird species on the
same study area using an index he developed. He based this index on observations of
indicators of breeding activity. These indicators included paired adults, adults carrying
nesting material or food, and the presence of fledglings. He related reproductive success
to basal area of various tree species using Canonical Correspondence Analysis (CCA).
He found black-throated green warbler, black-throated blue warbler, and red-eyed vireo
reproductive success associated with above average basal area of American beech. The
only other species reported in Table 5.1 that showed an association between reproductive
success and any environmental variable were American redstart and northern parula.
Reproductive success for these two species was associated with above average basal area
of softwood understory.
91
Black-throated green warblers exhibited the strongest foraging associations with
American beech. This led to my prediction that if any bird species were to exhibit a
positive relationship between beech basal area and its own presence or beech basal area
and reproductive success, it would be black-throated green warbler. This was indeed the
case with this species being the only focal bird to exhibit a significant (p<0.05) result.
Following this through to the data of Gunn (2002), black-throated green warbler emerges
as one of the species showing reproductive success associated with above average beech
basal area. These lines of evidence suggest a relationship between foraging behaviour,
landscape distribution, and reproductive success.
Black-throated blue warbler also exhibited strong foraging associations with
American beech. While its presence was not associated with beech basal area,
reproductive success data (Gunn 2002) demonstrated an association with higher than
average beech basal area. A variety of explanations might apply here, but a particularly
interesting consideration is the existence of a dominance hierarchy. Morse (1989)
suggests that of northern hardwood bird species, black-throated green warbler holds the
dominant position in the hierarchy. Such a dynamic might explain the random
relationship between black-throated blue warbler presence and beech basal area in spite
of selective use of beech and higher reproductive success associated with higher basal
area of beech. Their settlement and presence on these sites might be inhibited by the
black-throated green warbler.
92
An alternative explanation might stem from the more generalized habitat
requirements of black throated blue warblers (Sherry and Holmes 1985). They have
observed that black-throated blue warblers have a less patchy distribution than blackthroated green warblers due to less specific habitat requirements. This might lead to
random settlement by black-throated blue warblers with respect to beech distribution.
Such a priori selection would not preclude a possible advantage of American beech with
respect to foraging success and reproductive success should adequate beech be available.
The results are more ambiguous for American redstart. Chapter 2 demonstrates
some selective foraging in American beech by this species depending upon the year.
This species also either avoids sugar maple as a foraging site or selection is neutral. Its
presence is associated with sugar maple basal area, and its reproductive success is
associated with basal area of softwood understory. Sherry and Holmes (1985) found that
this species, like the black-throated blue warbler, has less specific habitat requirements
and a less patchy distribution than black-throated green warblers.
It was not surprising that least flycatcher did not exhibit an association between
the abundance of any tree species and either its own presence at a point or reproductive
success. I included this species in my focal group because its primary foraging strategy
(mid-air hawking) was the least likely to exhibit a dependence on a particular species of
tree, thus providing a contrast to the foliage dependent foragers.
93
Two non-focal species, northern parula and magnolia warbler, demonstrated an
association (p<0.05) between their presence at a point and the basal area of beech. Gunn
(2002) found that northern parula reproductive success was associated with softwood
understory rather than beech basal area. While it might have selected territories based
upon beech abundance it is possible that a threshold value was reached and not limiting
to productivity. There were no other significant relationships between the presence of
any bird species and the abundance of any tree species at a point.
In addition to black-throated green and black-throated blue warbler reproductive
success being related to beech abundance, Gunn (2001) found the same to be true for redeyed vireo. This species did not show an association between presence at a point and
beech abundance. It did demonstrate a tendency to forage in American beech in the one
year that I recorded incidental observations for this non-focal species. Eight of ten
foraging observations made on this species were in beech. With respect to presence at a
point and productivity, this species represents a relationship that is opposite to northern
parula. Although red-eyed vireo might not select a point with higher abundance of beech,
it does show higher reproductive success in association with this species.
The lines of evidence from my work and the work of Gunn (2002) are particularly
striking for black-throated green warbler. Black-throated green warbler forage
selectively (p<0.05) in American beech and was the only focal bird species to
demonstrate a significant (p<0.05) relationship between its presence and beech
abundance. Black-throated green warbler also showed a significant association between
reproductive success and beech abundance in a Canonical Correspondence Analysis
(Gunn 2002).
94
Previous findings that black-throated green warblers are more patchily distributed
due possibly to more specific habitat requirements (Holmes and Sherry 1985) including
tree species selection (Morse 1976) are interesting in light of my own results. It would
have been predicted that the least plastic species with respect to foraging requirements
should have exhibited the stronger association with a key resource in its habitat selection,
foraging behaviour, and reproductive success. As a socially dominant warbler (Morse
1989), this species should have had the ability to exercise this site specificity over birds
such as black-throated blue warbler. As noted previously, black-throated blue warblers
selected beech for foraging, enjoyed higher reproductive success in areas with higher
abundance of beech, yet did not settle in areas with high abundance of beech, perhaps due
to displacement.
The evidence for a behavioural process influencing landscape pattern is
compelling, but does result from a-posteriori relation of temporally and spatially parallel
studies. The next step would be a study designed to test landscape patterns of settlement
and productivity in terms of selective foraging behaviour among the same individual
birds using the predictions proposed in this synthesis.
95
Table 5.1. Logistic regression of bird presence on tree basal area, significant values
(p<0.05) in bold, significant values for focal bird species in bold and italics.
Bird Species
amre
mnwa
scta
yrwa
btbw
revi
bhvi
btgw
cswa
nopa
phvi
lefl
American beech
0.61
0.03
0.60
0.20
0.63
0.69
0.56
0.04
0.65
0.02
0.69
0.88
sugar maple
0.01
0.71
0.60
0.74
0.62
0.74
0.68
0.85
0.06
0.35
0.29
0.36
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yellow birch
0.82
0.17
0.60
0.78
0.04
0.57
0.55
0.70
0.22
0.60
0.93
0.16
Chapter 6: Scientific Conclusions and Management Implications
Foraging Site Selection and Success
Tree species use by four species of foraging songbirds in a northern
temperate mixed-wood forest was observed over four consecutive breeding
seasons. American beech on the mm-grid was selected out of proportion to its
availability by black-throated green warbler, black-throated blue warbler,
American redstart, and least flycatcher, in 11 of the possible 16 cases involving
these 4 bird species over 4 years (Figures 3.3-3.6). Yellow birch, sugar maple,
and balsam fir, were selectively avoided by these same birds in 9, 8, and 10 cases
respectively (Figures 3.1-3.6).
Rates of foraging differed significantly among tree species in some years for the
black-throated blue and black-throated green warblers, but the results were less consistent
than the selective use results (Tables 3.4-3.8). Attacks per unit time is a straight forward
measure of rate in temporal units. Attacks per flight is a spatial measure, as these are
attacks performed within a foraging patch (a unit of branch and foliage) following the
arrival flight and prior to the departure flight. The more conservative post-hoc Nemenyi
test shows that the black-throated green warbler was the only bird species in all years to
demonstrate differential foraging success (Tables 3.4 –3.5). This forage rate was in terms
of units of time only. The less conservative multiple application of post-hoc MannWhitney-U tests (Sheskin 1997) shows significant differences in foraging rate measured
in terms of time for black-throated green warbler in 1999 and in terms of flight numbers
in 1999 and 1996. The general trend for these post-hoc tests shows higher foraging rates
in beech. Black-throated blue warbler is the only other species to demonstrate any
97
difference in a foraging rate measure among tree species. In 1996, attacks per minute
were higher in beech than maple using the less conservative Mann-Whitney post-hoc test
for multiple comparisons. Holmes and Robinson (1981) found no difference in foraging
rates for black-throated blue warbler or American redstart. They did not present results
for black-throated green warbler.
Beech basal area was very low due to its complete absence at most grid
points on the im-grid and consequently is unlikely to be available for selection.
Maple seemed to replace beech as the selected tree, and birch was still either
avoided or selection was neutral (Figures 3.1-3.2) . Least flycatcher selected
maple in both years that I conducted work in the intensively managed grid, 1997
and 1999. Black-throated blue warbler selected maple in 1999 and black-throated
green selected maple in 1997. There were no significant differences among tree
species for either measure of foraging rate for any of the bird species on the imgrid.
In spite of general patterns of selective use of beech, there was some variation
among years that would not have been captured in an analysis that pooled years. The
black-throated blue warbler, American redstart, and least flycatcher broke this pattern in
1999 on the mm grid. Black-throated blue warbler neither selected nor avoided
American beech. American redstart selected yellow birch and avoided American beech,
and least flycatcher selected sugar maple and neither selected nor avoided American
beech (Figures 3.3-3.4). Black-throated green warbler broke the general pattern of
American beech selection in 1998, neither selecting nor avoiding this species (Figure
3.6). In summary, black-throated green warbler departed from the use patterns seen in
98
the other three bird species in two different years. The Black-throated green warbler was
selecting American beech in 1999 when the other three bird species were avoiding or
randomly using this species. The black-throated green warbler was using American
beech randomly in 1998 when the other three species were selectively using this species.
The latter pattern is especially interesting in light of the arthropod data and the
following observations. Balsam fir was selectively used in only one year (1998) by one
bird species (black-throated green warbler) considering both the im and mm-grids (Figure
3.6). This species has the strongest association with coniferous trees (Morse 1993),
therefore, it is not surprising that of all focal species this would demonstrate a positive
association with a balsam fir. While selective use of balsam fir in one year of four not
strong support for this pattern, one interesting conjecture is there might be a structural
similarity shared by beech and fir or a behavioural trait on the part of the black-throated
green warbler’s foraging repertoire more suited to the morphology of these two tree
species.
Another conjecture is related to the overall lower densities of arthropods on the
mm-grid in 1999 versus 1998 (Tables 4.1-4.2). Perhaps it is only in years of low
arthropod density that there is some advantage to foraging in American beech.
Unfortunately, I do not have arthropod data from 1996 and 1997 to compare with the
typical pattern of selective foraging in American beech. My post-hoc prediction would
be that arthropod densities were atypically high (considering the four year span of my
work) in 1998 and that densities of 1999 would be comparable to 1996 and 1997.
Araneida is unique in several aspects. It is the most abundant arthropod overall in
tree foliage (Tables 4.1-4.5), it is the most abundant arthropod in stomach samples
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(Figure 3.11), and it is a predator of many other arthropod prey. It is also the only
arthropod to vary significantly in its relative density between American beech and balsam
fir over the two years. Araneida density in terms of units of foliage area was higher in
balsam fir than in American beech, sugar maple, and yellow birch (p<0.05) in 1999
(Table 4.4). Araneida density was equal in American beech and balsam fir in 1998 and
higher (p<0.05) in yellow birch compared with sugar maple, balsam fir, and American
beech (Table 4.4).
The black-throated green warbler selected balsam fir as a foraging site in a year
(1988) when overall arthropod availability was higher across all tree species and araneida
density in balsam fir was lower relative to all other tree species. One explanation for the
avian foraging pattern might be related to easier location of arthropod prey by the
foraging bird in an environment free of a competing predator, araneida. Lepidopteran
larvae were more abundant in balsam fir than in the other tree species in 1999 on the mmgrid (Table 4.1), though this difference was not statistically significant (p>0.05). This is
worth consideration given its know importance in the diet of insectivorous passerines
(Morse 1993, Homes 1994, Sherry and Holmes 1997).
I propose a general model with three categories of tree species utility for foraging
birds. At one extreme is American beech is most often selected for foraging by 4 species
of forest passerine. One of these passerines, black-throated green warbler, is particularly
sensitive to beech showing higher foraging success in this tree species. The next
category of foraging utility is filled by sugar maple. When beech is not available, maple
is selected out of proportion to its abundance, but foraging success does not differ at any
time in the maple versus the other tree species. It is still possible that there is an
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advantage in maple in terms of energy expended even in the absence of higher prey
yields. The third category of utility is filled by birch and fir, both species that are rarely
selected as a foraging site even in the intensively managed grid where beech is not
readily available.
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Evaluation of the Arthropod Hypothesis
All arthropod orders preyed upon by the focal songbirds are found in the clip
samples obtained from the trees. This allays the concern that a critical prey item might
not be sampled from one of the tree species thus leading to erroneous conclusions about
selective foraging causality. While probability of detection among stomach contents may
vary among arthropod orders, it is less likely that exoskeletal remains of one particular
order would consistently have been missed in 42 stomach samples.
These results help ensure that arboreal arthropod sampling did not exclude
a component of the warblers’ diet. The potential does exist that a critical prey
species is not represented in the arthropod community sample as both the prey
data and community data are identified to order. Wolda (1990) states that
taxonomic pooling of the arthropod prey base is justified if those groups pooled
are not likely to exhibit physical or behavioural differences from the perspective
of the foraging bird. Holmes and Robinson (1981) performed similar work on
some of the same bird and tree species in New Hampshire and found
identification of the arthropod prey base to taxonomic order adequate.
102
I found higher densities of several orders of arthropod and higher order richness
in yellow birch compared with American beech and sugar maple (Table 4.4). Araneida
densities ranged from a mean of 2.2 per cm2 in yellow birch to 2.0 per cm2 in American
beech, and 1.93 per cm2 in sugar maple. These density results are based on arthropods
per total unit area of leaf sampled in the tree. I also calculated densities based upon the
arthropods found in the clip samples, and found fewer cases of significant differences
among tree species (Table 4.5).
I am confident that I can reject the arthropod hypothesis for selective foraging
observed in American beech. Densities and diversities of arthropod prey are consistently
higher on yellow birch using either method (per unit of leaf area or foliage volume) of
calculation. In spite of this, yellow birch was usually avoided by foraging songbirds.
Lepidopteran larvae are notably absent from the stomach contents data and the
arthropod community data as well. I would be more concerned with my methods if one
of these components of my work had demonstrated a significant presence of this
important insectivorous passerine prey item (Morse 1993, Homes 1994, Sherry and
Holmes 1997). Quite to the contrary, I interpret this as a potentially significant result
with possible explanatory power in relation to regional differences (discussed below) in
foraging patterns.
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Evaluation of the Morphology Hypothesis
This research introduces the first comprehensive study of selective foraging in
deciduous tree species by insectivorous birds that is able to isolate the two dominant
explanatory hypotheses from one another. The American beech had lower abundances of
all arthropod prey found in the focal birds’ diets, while yellow birch had higher
abundances of these prey items. Yellow birch also had the higher arthropod richness and
total arthropod abundance outside of primary prey items than American beech and sugar
maple. I reject the arthropod hypothesis in those cases where birds foraged selectively or
at higher rates of success in American beech and sugar maple, while avoiding yellow
birch.
Previous work has sought the causal process responsible for selective foraging
behaviour by birds in particular species of trees, and has found mixed results (see review
in Chapter 1). Holmes and Robinson (1981) present evidence for both the arthropod and
tree morphology hypotheses. While their evidence supports the arthropod hypothesis, the
tree morphology hypothesis is not excluded. In contrast, my own results do exclude one
of the hypotheses (the arthropod hypothesis), which leads me to invoke the tree
morphology hypothesis for explanation of the primary foraging patterns that I observed.
Rejection of this primary hypothesis has led me to consider the morphology
hypothesis alternative hypothesis involving leaf and branch morphology and foraging
behaviour since beech and birch do have contrasting morphologies (Horn 1971).
104
The morphology hypothesis is based in part upon a description of northern
temperate tree morphology given by Horn (1971). He determined that the genus Betula
(including yellow birch) differs from American beech and sugar maple. Birch has
branches arranged in multiple layers, while beech and maple branches are arranged in a
monolayer. Put in other terms, the foliage of beech and maple is condensed in a plume of
leaves in one layer of branches, and the foliage of birch is arranged in multiple layers on
branches spaced vertically along the tree trunk.
The terms monolayer and multilayer can be misleading if viewed at the wrong scale.
Horn classifies beech and maple as monolayered trees and birch as a multilayered tree.
This is correct when speaking of branches, but it is not an appropriate classification for
leaf arrangement at the within-branch scale. As Plates 6.1-6.8 indicate the
“monolayered” American beech and sugar maple are actually multilayered at the scale of
the branch while the “multilayered” yellow birch is actually mono-layered at this scale.
Holmes and Robinson (1981) further confound the situation in their paper by
incorrectly stating that the leaves, not just the branches, of beech and maple are
monolayered while the leaves of birch are multilayered. These are very important scalar
distinctions, because I contend that the within branch scale is more relevant to the
efficiency of a foraging bird.
Considering the scale of a foraging bird, a mono-layer would functionally be a
multiple layered offering of substrate, while. A mono-layered tree species has its leaves
in several planes within reach of a foraging bird advancing by hops down a branch or
twig
105
Considering the spatial scale of a bird foraging from a branch, the monolayer
actually has multiple layers of leaves due to overlapping growth of twigs and branches
through several planes. Multiple foraging patches of foliage exist in three dimensions
relatively short within-branch flights or hops away. The branches of a multilayered tree
have only a single layer of leaves available to a bird foraging along that branch (see
Plates 6.1-6.8). The multi-layered (at the whole tree scale) yellow birch possesses layers
reachable only through a relatively longer flight to another branch or foraging patch.
The data of Table 4.6 reflect this condition with much higher total surface area of
leaves available along a unit length of branch within the 1 meter search area of a foraging
insectivorous passerine (Robinson and Holmes 1982). Table 4.6 reports the mean
numbers of leaves per unit length of branch sampled with the pole pruners, the mean
surface area per leaf, and the mean leaf area per unit length of branch sampled for each
tree species. Yellow birch had the smallest leaves and the fewest per unit length of
branch sampled. These factors combined to produce a mean leaf area per unit length of
branch sampled that was approximately half of the mean leaf area per unit length of
branch sampled for American beech. American beech leaves were slightly smaller than
sugar maple leaves on average, but the greater number of them per unit length of branch
compensated for this and gave beech the highest overall leaf area per unit length of
branch sampled.
106
Horn (1971) also demonstrated that birch leaves are randomly spaced while maple
and beech leaves are evenly spaced. The vertical separation of branches in a multilayer
tree allows for random spacing of the leaves as light is able to penetrate to each layer at
an angle. Monolayered trees have higher densities of leaves along a given length of
branch than multilayered trees, therefore, leaves are spaced evenly in the dense foliage of
a monolayer to minimize overlap and shading. I propose that even spacing of the
monolayer leaves would provide more a predictable foraging environment than the
random leaf arrangement along the branch of a multilayered tree. Another benefit of the
dense cluster of leaves in a monolayer might be related to the ability of a leaf gleaning
bird to approach prey without causing them to flush prematurely. American beech
foliage might also offer a safer place to forage for the birds, though higher foraging rates
of foraging success in American beech (Tables 3.4-3.8) suggest that foraging in this
species is not a by product of another use of the tree such as a source of refuge or a place
or a place to use for display. An advantage to foraging in American beech could still be
related to avian predator avoidance if the bird is able to devote more energy and time to
foraging, thus resulting in greater foraging efficiency. If this were the case, the
morphology hypothesis would still be supported.
As previously discussed, American beech has a higher volume of foliage in
multiple layers (see Table 4.6, Plates 6.1-6.8, and Horn 1971). A bird capable of
foraging in multiple planes while hopping along a branch would be better able to exploit
the resources in American beech. While the glean manoeuvre is suited for yellow birch,
the addition of the hover manoeuvre would be needed to exploit resources within the
three dimensional foraging patches of American beech. I predicted a priori higher
107
proportions of the hover manoeuvre in American beech than in yellow birch. My focal
birds showed either a lower (p<0.05) use of the hover in yellow birch (where leaves are
located below a bird), or a greater (p<0.05) use of the hover in American beech (where a
greater proportion of leaves are located above a foraging bird rather than below it) (Table
3.10 and Figures 3.7-3.10).
The glean manoeuvre was used to a similar extent across the three broad-leaved
tree species by the two Dendroica species. Black-throated blue warblers and American
redstarts used the hover manoeuvre in greater proportions than expected by chance in
American beech. Black-throated green warblers and American redstarts used the hover
manoeuvre in proportions lower than expected by chance in birch (Table 3.10 and
Figures 3.7-3.10).
It was particularly striking that least flycatcher used a higher proportion of hovers
in American beech. This species uses the hawk manoeuvre more than any of the other
focal birds, yet it not only foraged selectively in American beech (3.4), but it also adjusts
its foraging strategy in the same fashion as do the other focal species. I view this as more
inferential evidence for the morphology hypothesis in explaining selective foraging in
American beech.
I propose that within the uni-planar foraging patch in yellow birch, it is primarily
the topside of the leaves that are available, while within multiple-planar foraging patch on
beech, both sides are available simultaneously at a relatively low cost to the foraging bird
as hovers are short within-branch manoeuvres. This could explain the significant use of
the hover and glean in beech and only the use of the glean in yellow birch . This
explanatory process requires a novel view of what constitutes a patch for these foraging
108
birds and how is this patch best exploited while a bird is searching. Dunning (1990)
urges just such consideration of patch definition in avian foraging studies.
Whelan (2001) found that black-throated green warblers, black-throated blue
warblers, and American redstarts foraged disproportionately on the upper surfaces of
yellow birch. Whelan (2001) also found the black-throated blue warbler and American
redstart foraged disproportionately on the upper surfaces of sugar maple leaves.
Although Whelan did not study American beech, sugar maple foliage structure is more
similar to American beech structure than yellow birch. Whelan’s results, therefore, lend
support to my contention that the yellow birch might be less suited to the hover
manoeuvre as this strategy is best used for leaf surfaces above a bird. His work
represents patterns of use of the tree species consistent with my own hypotheses and
interpretations of my data.
Whelan (2001) speaks in terms similar to my own when he refers to distinct tree
species offering specialized foraging microhabitats that enhance niche diversity. While
some of my hypotheses here clearly need further testing, perhaps in an experimental
design that includes aviary work, I have ample evidence that tree species morphologies
offer different foraging opportunities and are likely the cause for the patterns of selective
use and avoidance that I observed.
109
Holmes and Robinson (1981) and Holmes and Schultz (1988) did not eliminate
the tree morphology hypothesis as a potential explanation. Based upon their
interpretation of Horn’s results, they contend that the multilayered birch would actually
offer more leaves to a bird foraging from any given location on a branch. This
interpretation does not make sense in light of Horn’s description of monolayer and
multilayer forms, therefore, I tested this assertion in the course of gathering our foliage
clip samples. As Plates 6.1-6.8 and Table 4.6 suggests, American beech, not yellow birch
has an optimal morphology for leaf-surface feeding passerines. Interestingly, in this
light, Holmes and Schultz would have actually demonstrated a case for the arthropod
hypothesis alone had their interpretation of the optimal morphologies matched my own.
Based upon their interpretation of the tree morphologies Holmes and Robinson (1981)
and Holmes and Schultz (1988) concluded that for some species of bird foraging in
yellow birch, both hypotheses 1 and 2 are responsible for selective use of that tree
species. It was my goal to isolate a situation where either one or the other but not both
could be invoked as the explanation for selective use of a particular tree species
110
Landscape Pattern and Process
My work in conjunction with the companion study performed by John Gunn
(2002) offers the first evidence for a local behavioural process influencing population
dynamics in a landscape. My work also offers the first evidence for a local behavioural
process explaining landscape patterns of species distribution. American beech was
selected as a foraging site by the focal birds in my own study and the bird with the
strongest association, black-throated green warbler, showed a strong association between
reproductive success and the presence of American beech across the landscape.
American beech was also a strong predictor of the presence of black-throated green
warbler in the landscape.
It is not hard to imagine that such a basic life process as foraging would have such
widespread and profound influence across multiple spatial scales. Our evidence suggests
that behavioural choices made at the organismal level do indeed ripple through multiple
scales of space and time across the landscape. I acknowledge that the evidence is not a
formal test, but rather a suggestive link worthy of further testing.
Discussion of different types of habitat selection, and mention here that this is a
major of apriori selection of landscape based upon beech and that it was by Green which
had the strongest associations with beech.
111
Regional Comparison
My work contrasts with similar work in New Hampshire that showed higher
selective use of yellow birch and higher arthropod densities in yellow birch versus
American beech. Holmes and Schultz (1988) concluded that differential arthropod
density among tree species is responsible for the higher selective use of yellow birch in
New Hampshire. I conclude that it is the morphology of the American beech coupled
with foraging manoeuvres that drives the selective use of the beech. Perhaps there is a
regional difference in the processes responsible for foraging site selection and success.
My work contrasts with the work of Holmes and Robinson (1981) with respect to
avian foraging patterns in American beech and yellow birch in a mature secondary
mixed-wood forest. I consistently found selective use of American beech and selective
avoidance or neutral use of yellow birch over 4 field seasons for the 4 species of bird I
studied in the moderately managed grid. Holmes and Robinson (1981) found the
opposite pattern with strong selective use of yellow birch and avoidance of American
beech. My results for the sugar maple on the moderately managed grid agree with the
results of Holmes and Robinson. This tree species was avoided or selection was neutral.
112
Holmes and Robinson (1981) documented higher densities (14 per 10,000 cm2) of
arthropod prey on yellow birch versus 8 per 10,000 cm2 for sugar maple and 5 per 10,000
cm2 for American beech. They cite this as support for the arthropod hypothesis regarding
the selective foraging they observed in yellow birch. Holmes and Schultz (1988)
evaluated the abundance of a particularly important prey item, Lepidoptera larvae.
Though they documented higher overall densities of larvae on beech, they determined
that the yellow birch had higher densities (approximately 1 per 10,000 cm2) of free living
larvae, the life stage available to leaf gleaning birds. Again this is cited as evidence in
favour of the arthropod hypothesis.
113
The arthropod densities per unit of leaf area of all tree species on my study sites
were over 30 % higher than the densities observed in New Hampshire. An interesting
speculation is that the more northerly latitude of my study site might support higher
densities in a shorter period of time due to the shorter summer period. Perhaps once an
arthropod prey population has exceeded a threshold level across all tree species, the only
way for a foraging bird to increase its capture rate is to maximize foraging efficiency in
relation to tree species leaf and branch morphology. Two previously mentioned
observations within this research might lend credibility to this hypothesis. The apparent
lack of a potentially critical resource, lepidopteran larvae, suggests an environment poor
in arthropod prey. Perhaps the New Brunswick forests were below a threshold value for
this prey item alone leading to a selective mechanism for increased foraging efficiency
through an optimal fit between foraging strategy and tree morphology. A microcosm for
this model might exist within my own work with the selective use of the balsam fir over
American beech by black-throated green warblers in 1988 (Figure 3.6). A higher overall
arthropod abundance in 1988, or conversely, a switch back to an optimal efficiency in
American beech in 1999 might be a demonstration of the morphology hypothesis.
114
If New Hampshire arthropod densities were calculated using leaf volume, the
disparity between the foraging patterns in the two areas would be even more evident.
Calculation of arthropod density using leaf volume within a bird’s search area would
deflate the effective availability of arthropods in American beech relative to yellow birch.
This would strengthen the speculation that there is some regional difference between the
study sites and that the arthropod hypothesis is the best predictor of the patterns in New
Hampshire, while the morphology hypothesis is the best predictor of the patterns in my
study.
Another comparison between the two study sites is the proportion of tree species.
American beech, sugar maple, and yellow birch were the dominant tree species on my
mm-grid and in the Hubbard Brook study area. Yellow birch basal area is, however,
approximately 1/3 of the basal areas of American beech and sugar maple on the mm-grid
in New Brunswick while it occurs in approximately equal proportions as American beech
and sugar maple in New Hampshire. Yellow birch is more abundant than American
beech and sugar maple on the im-grid in New Brunswick, with American beech
practically nonexistent. The proportions found on the mm-grid might suggest that part of
the pattern of yellow birch avoidance could be due to it being below a threshold value.
This is not likely given the relative proportions of yellow birch, American beech, and
sugar maple on the im-grid and the same pattern of yellow birch avoidance by foraging
birds as seen on the mm-grids.
115
Forest Management
I concur with the forest management implications suggested by Holmes and
Robinson (1981) and Whelan (2001). They propose that forest management practices
that either cull or selectively harvest particular tree species compromise the resource base
and niche diversity available to forest passerines.
My proximate management recommendation is for the maintenance of American
beech in our industrial forests as it appears to offer unique and important foraging
resources to insectivorous passerines. In addition to its use by songbirds it is well known
that the beech offers an important mast crop to a variety of small and large mammals
(Degraaf and Yamasaki 2001). Unfortunately, American beech is intentionally removed
by forest managers throughout its range in Canada and the United States due to its low
commercial value and susceptibility to disease. This proximate recommendation is not a
novel suggestion given other work across other taxonomic groups already suggesting the
importance of this tree species.
116
In light of this, I offer a more theoretical, ultimate management recommendation
that should transcend the particular forest type I studied. I have demonstrated that it is
not merely important to maintain American beech, nor is it merely important to maintain
a diversity of tree species. By linking reproductive success to fine-scale morphological
differences I have demonstrated that it is important to maintain a diversity of tree
morphological types in the landscape. Moreover, our perception of what constitutes a
novel tree morphological type should be tuned to perhaps previously unnoticed
seemingly minor differences in micro-scale vegetation structure. I have also
demonstrated the potential folly in extrapolating results even within seemingly similar
forest types separated by only several hundred kilometres.
117
Future Research
At the first opportunity available, I would like to construct aviary experiments
with the focal birds after the methods of Whelan (1989a, 1989b, 2001) and Parrish
(1995a and 1995b). Whelan’s work especially was remarkably close to my own work
with tests of forage site selection and forage manoeuvres on sugar maple and yellow
birch by the same focal bird species. His work was tantalizing in its similarity combined
with what was to me a conspicuous absence of American beech. Sugar maple foliage is
similar to American beech, or at least more so than yellow birch, therefore, relevant
arguments already exist within his work.
An experimental design adjusting prey availability above and below physiological
thresholds would be an elegant test of my hypothesis that low prey availability will cause
a bird to switch to an optimal foraging strategy based upon the morphology hypothesis.
Prior to that I would like to confirm or refute selective foraging in American beech by
birds from the New Brunswick study sites and birds from New Hampshire and coastal
Maine. This would allow the type of regional comparisons made by Parrish (1995a and
1995b).
118
Plate 6.1. American beech branch and twig morphology within approximately 1 m3
foraging patch, total leaf area: 3224 cm2.
119
Plate 6.2. Yellow birch branch and twig morphology within approximately 1 m3 foraging
patch, total leaf area: 1550 cm2.
120
Plate 6.3. Sugar maple branch and twig morphology within approximately 1 cubic meter
foraging patch, total leaf area: 2860 cm2.
121
Plate 6.4. Yellow birch (left) and American beech branch, twig, and leaf morphology
removed from tree.
Plate 6.5. Sugar maple (left) and American beech branch, twig, and leaf morphology
removed from tree.
122
Plate 6.6. American beech branch morphology on tree.
Plate 6.7. Yellow birch branch morphology on tree.
123
Plate 6.8. Sugar maple branch morphology on tree.
124
Appendix 1
Use of Syrup of Ipecac (Ipecacuanha) as an Emetic for Obtaining
Diet Samples of Several North American Passerines *
* authors are Antony W. Diamond and Peter S. McKinley
A non-toxic and non-lethal means to acquire such a sample is important for
ethical, legal, and study design considerations. Methods previously used in other studies
have included analysis of fecal samples (Davies 1977), flushing the digestive tract with a
saline solution (Moody 1970), forced regurgitation with water (Rosenberg and Cooper
1990), and forced regurgitation with an emetic, most notably, tartar emetic (antimony
potassium tartrate) (Tomback 1975, Zach and Falls 1976, Gavett and Wakeley 1986,
Poulin et al 1993).
Most methods are either inefficient with respect to both time and quality of
sample, or are toxic and potentially lethal to the bird. For example, Tomback (1975)
observed a response period between 10 and 25 minutes depending upon the dosage level
of tartar emetic. Zach and Falls (1976) captured 41 Ovenbirds and administered tartar
emetic to 20. They were all maintained in captivity, and at the end of one week, 50% of
the treated birds had died while only 14.3% of the untreated birds had died. While Poulin
et al (1993) reported the seemingly low mortality of 2.0% with the use of tartar emetic,
this amounted to 70 birds in their study.
Syrup of Ipecac (Ipecacuanha) is an infrequently used, but promising alternative
to tartar emetic. Ipecac is a natural extract from the roots of the rubiaceous plants
Cephaelis ipecacuanha or C. acuminata (Martindale 1977). It is used as an emetic on
children as young as six months to induce emesis after consumption of a poisonous
125
substance. Ipecac induces emesis by two means. It irritates the stomach lining and
directly stimulates chemoreceptors that induce the emesis response as well. Ipecac does
not produce systemic toxicity (Canadian Pharmaceutical Association, 1997).
Diamond and Fayad compared the mortality and effectiveness of tartar emetic
and ipecac on landbirds in Kenya (unpublished manuscript). They found ipecac to be as
effective as tartar emetic, while only the birds treated with ipecac showed no mortality.
Radke and Frydenhall (1974) used syrup of ipecac on the granivorous House Sparrow,
Passer domesticus, with no success. A concentration of 50% produced no emesis, while
higher concentrations resulted in death due to suffocation from the high viscosity of the
syrup.
We used a dose to body weight ratio of 0.1 cc per gram of body mass based on the
work of Diamond and Fayad (unpublished manuscript). Syrup of ipecac was delivered
with a syringe attached to 2mm physiological tubing. The tubing was inserted into the
stomach through the oesophagus. The bird was placed in an opaque plastic container
with a lid immediately following this treatment.
In the summer of 1998 the emetic was administered to 2 American Redstarts, 5
Black-throated Blue Warblers, and 7 Black-throated Green Warblers. One of the Blackthroated Green Warblers was recaptured approximately two weeks following its first
capture. The bird was treated with the emetic again so that for 1998 there were 15 total
treatments. With the exception of one female Black-throated Blue Warbler, all birds
captured in 1998 were male. Stomach contents were recovered 100% of the time.
During the 1999 field season the emetic was administered to 19 Black-throated
Blue Warblers and 11 Black-throated Green Warblers. Two of the Black-throated Blue
126
Warblers were recaptured approximately two weeks after their first capture. These birds
were treated with the emetic again so that for 1999 there were 32 total treatments. All
birds captured in 1999 were male. Stomach contents were recovered 100% of the time.
Treatments for both years totaled 47.
Stomach contents were regurgitated within 30 seconds. Identifiable prey remains
in the stomach samples included arthropod wings, legs, and other parts of the
exoskeleton. In most cases identification to order was possible. Exoskeletal remains of
several arthropod orders were recovered from all samples. Orders identified include
Coleoptera, Diptera, Hemiptera, Lepidoptera, Thysanoptera, and Hymenoptera.
The birds required virtually no recovery time. All handled individuals flew from
the hand and resumed normal activities immediately, including foraging and singing.
The recaptured birds showed similar quick recovery and behavior.
127
References Cited
Abbott, I., and P. Van Heurck. 1985. Tree species preferences of foraging birds in Jarreh
Forest in Western Australia. Australian Wildlife Research 12: 461-466.
Airola, D.A., and M.H. Barrett. 1985. Foraging and habitat relationships of insectgleaning birds in a Sierra Nevada mixed-conifer forest. Condor 87: 205-216.
Ambuel, B., and S.A. Temple. 1983. Area-dependent changes in the bird communities
and vegetation of southern Wisconsin forests. Ecology 64: 1057-1058.
Anderson, B.W., M.D. Ohmart, and J. Rice. 1983. Avian and vegetation community
structure and their seasonal relationships in the lower Colorado River valley. Condor
85: 392-405.
Anderson, S.H., and H.H. Shugart Jr. 1974. Habitat selection of breeding birds in an east
Tennessee deciduous forest. Ecology 55: 828-837.
Bart, J., M.A. Fligner, and W. I. Notz. 1998. Sampling and statistical methods for
behavioural ecologists. Cambridge University Press, New York, NY., USA.
Bayne, E. M. and K.A. Hobson. 1997. Comparing the effects of landscape fragmentation
by forestry and agriculture on predation of artificial nests. Conservation Biology
11:1418-1429.
Beedy, E.C. 1981. Bird communities and forest structure in the Sierra Nevada of
California. Condor 83: 97-105.
Belisle, M., and A. Desrochers. 2002. Gap-crossing decisions by forest birds: an
empirical basis or parameterizing spatially-explicit, individual-based models.
Landscape Ecology. 17: 219-231.
Bell, G.W., S.J. Hejl, and J. Verner. 1990. Proportional use of substrates by foraging
birds: model considerations on first sightings and subsequent observations. Pages
161-165 in M.L. Morrison, C.J. Ralph, J. Verner, and J.M. Jehl Jr., editors. Avian
Foraging: Theory, Methodology and Applications. Studies in Avian Biology No. 13.
The Cooper Ornithological Society. Los Angeles, CA., USA.
128
Bibby, C.J., N.D. Burgess, and D.A. Hill. 1993. Bird Census Techniques. Academic
Press. New York, N.Y., USA.
Block, W.M. 1988. Biogeographic variation in foraging ecologies of breeding and
nonbreeding birds in oak woodlands. Pages 264-269 in M.L. Morrison, C.J. Ralph, J.
Verner, and J.M. Jehl Jr., editors. Avian Foraging: Theory, Methodology and
Applications. Studies in Avian Biology No. 13. The Cooper Ornithological Society.
Los Angeles, CA., USA.
Blondel, J., C. Ferry, and B. Frochot. 1981. Point counts with unlimited distance. Pages
414-420 in C.J. Ralph and J.M. Scott, editors. Estimating Numbers of Terrestrial
Birds. Studies in Avian Biology no. 6. The Cooper Ornithological Society. Los
Angeles, CA., USA.
Bourque, J., and M.-A. Villard. 2001. Effects of selection cutting and landscape-level
harvesting on the reproductive success of two Neotropical migrant bird species.
Conservation Biology 15: 184-195.
Bowman, J. 2000. The spatial structure of small-mammal populations in a managed
forest. Ph.D. thesis. University of New Brunswick, Fredericton, NB., Canada.
Bowman, J., G. Forbes, and T. Dilworth. 2000. Landscape context and small-mammal
abundance in a managed forest. Forest Ecology and Management 140: 253-259.
Bowman, J. and G. Forbes. and T. Dilworth. 2001. The spatial component of variation in
small-mammal abundance measured at three scales. Canadian Journal of Zoology 79:
137-144.
Briskie, J.V. 1994. Least flycatcher (Empidonax minimus). In The birds of North
America, No. 99 (A. Poole and F. Gill, eds.). The Academy of Natural Sciences,
Philadelphia, PA, and the American Ornithologists’ Union, Washington, D.C., USA.
Brittingham, M.C., and S.A. Temple. 1983. Have cowbirds caused forest songbirds to
decline? Bioscience 33: 31-35.
Cody, IM.L. 1981. Habitat selection in birds: the role of vegetation structure,
competitors, and productivity. Bioscience 31: 107-111.
Cooper, M.J., and M.C. Whitmore. 1990. Arthropod sampling methods in ornithology.
Pages 29-37 in M.L. Morrison, C.J. Ralph, J. Verner, and J.M. Jehl Jr., editors. Avian
foraging: theory, methodology, and applications. Studies in avian biology no. 13.
Cooper Ornithological Society, Los Angeles, CA., USA.
129
Cumming, E.E. 1994. Songbird habitat use in Saskatchewan old-growth boreal mixed
wood forest. M.Sc. thesis, U. of Saskatchewan, Saskatoon, Sask., Canada.
DeGraaf, R.M., and M. Yamasaki. 2001. New England Wildlife: habitat, natural history,
and distribution. University Press of New England. Hanover, NH., USA.
Diamond, A.W. 1999. Concluding remarks: content versus context in forest bird research.
Pages 139-143 in A.W. Diamond and D.N. Nettleship, editors. Biology and
Conservation of Forest Birds, Society of Canadian Ornithologists Special Publication
no. 1. Fredericton, NB., Canada.
Dodge, K.M., M.C. Whitmore, and E.J. Harner. 1990. Analyzing foraging use versus
availability using regression techniques. Pages 319-324 in M.L. Morrison, C.J. Ralph,
J. Verner, and J.M. Jehl Jr., editors. Avian Foraging: Theory, Methodology and
Applications. Studies in Avian Biology No. 13. The Cooper Ornithological Society.
Los Angeles, CA., USA.
Dunning, J.B. 1990. Meeting assumptions of foraging models: an example using tests of
avian patch choice. Pages 462-470 in Morrison, M.L., C.J. Ralph, J. Verner, and
J.MM. Jehl jr., editors. Avian Foraging: Theory, Methodology and Applications.
Studies in Avian Biology No. 13. The Cooper Ornithological Society. , Los Angeles,
CA., USA.
Faaborg, J., M. Brittingham, T. Donovan, and J. Blake. 1993. Habitat fragmentation in
the temperate zone: a perspective for managers. Pages 331-338 in D.W. Finch and
P.W. Stangel, editors. Habitat fragmentation in the temperate zone: a perspective for
managers. U.S. Department of Agriculture Forest Service Rocky Mountain Forest
Range Experimental Station, General Technical Report Rm- 229. Fort Collins CO.,
USA.
Farina, A. 1997. Landscape structure and breeding bird distribution in a subMediterranean agro-ecosystem. Landscape Ecology. 12: 365-378.
130
Forman, R.T.T., A.E. Galli, and C.F. Leck. 1976. Forest size and avian density in New
Jersey woodlots with some land use implications. Oecologia 26: 1-8.
Fortin, M.-J., P. Drapeau, and P. Legendre. 1989. Spatial autocorrelation and sampling
design in plant ecology. Vegetatio 83: 209-222
Franzreb, K.E. 1978. Tree species used by birds in logged and unlogged mixedconiferous forests. Willson Bulletin 90: 221-238.
Freedman, B., C. Beauchamp, I.A. McLaren, and S.I. Tingley. 1981. Forestry
management practices and birds in a hardwood forest in Nova Scotia. Canadian Field
Naturalist 95: 307-311.
Freemark, K. and B. Collins. 1992. Landscape ecology of birds breeding in temperate
forest fragments. Pages 443-454 in J.M. Hagan III and D.W. Johnston, editors.
Ecology and conservation of Neotropical migrant landbirds. Smithsonian Institution
Press, Washington, D.C., USA.
Freemark, K.E. and H.G. Merriam. 1986. Importance of area and habitat heterogeneity to
bird assemblages in temperate forest fragments. Biological Conservation 36: 115-141.
Galli, A.E., C.F. Leck, and R.T.T. Forman. 1976. Avian distribution patterns in forest
islands of different sizes in New Jersey. Auk 93: 356-364.
Gates, J.E., and L.W. Gysel. 1978. Avian nest dispersion and fledging success in fieldforest ecotones. Ecology 59: 871-883.
Gilpin, IM. 1996. Metapopulations and wildlife conservation: Approaches to modelling
spatial structure. Pages 11-27 in D.M. McCullough, editor. Metapopulations and
wildlife conservation. Island Press, Washington, D.C.,USA.
Gobeil, J-F., and M.-A. Villard. 2002. Permeability of three boreal forest landscape types
to bird movements as determined from experimental translocations. Oikos. 98: 447458.
Greenberg, R., C.E. Gonzales, P. Bichier, and R. Reitsma. 2001. Nonbreeding habitat
selection and foraging behavior of the black-throated green warbler complex in
southeastern Mexico. The Condor. 103: 31-37.
131
Greenberg, M., and J. Gradwohl. 1980. Leaf surface specializations of birds and
arthropods in a Panamanian forest. Oecologia 46: 115-124.
Gunn, J.A., 2002. Landscape and Local Effects of Industrial Forestry on the
Reproductive Activity of Forest Songbirds in Northwestern New Brunswick, Canada.
Ph.D. thesis, University of New Brunswick, Fredericton, NB., Canada.
Gunn, J.A., A. Desrochers, M.-A. Villard, J. Bourque, and J. Ibarsabal. 2000. Playbacks
of mobbing calls of black-capped chickadees as a method to estimate reproductive
activity of forest birds. Journal of Field Ornithology 71(3): 473-483.
Hagan, J.M. III, P.S. McKinley, A.L. Meehan, and S.L. Grove. 1997. Diversity and
abundance of landbirds in a north-eastern industrial forest landscape. Journal of
Wildlife Management 61: 718-735.
Hagan, J.M., W. M. Vander Haegen, and P. S. McKinley. 1996. The early development
of fragmentation effects on birds. Conservation Biology 10: 188-202.
Hanski, I. 1994. Patch-occupancy dynamics in fragmented landscapes. Tree 9: 131-195.
Harris, L.D. 1988. Edge effects and conservation of biotic diversity. Conservation
Biology 2: 330-332.
Hayak, L.-E. C., and M.A. Buzas. 1997. Surveying Natural Populations. Columbia
University Press, New York, NY., USA.
Hejl, S.J., J. Verner, and G.W. Bell. 1990. Sequential versus initial observations in
studies of avian foraging. Pages 166-173 in M.L. Morrison, C.J. Ralph, J. Verner, and
J.M. Jehl Jr., editors. Avian Foraging: Theory, Methodology and Applications.
Studies in Avian Biology No. 13. The Cooper Ornithological Society. Los Angeles,
CA., USA.
Hinsley, S. A. 2000. The costs of multiple patch use by birds. Landscape Ecology. 15:
765-775.
Holmes, R.T. 1994. Black-throated blue warbler (Dendroica caerulescens). In The
birds of North America, No. 87 (A. Poole and F. Gill, eds.). The Academy of Natural
Sciences, Philadelphia, PA, and the American Ornithologists’ Union, Washington,
D.C., USA.
Holmes, R.T., R.E. Bonney Jr., and S.W. Pacala. 1979. Guild structure of the Hubbard
Brook bird community: a multivariate approach. Ecology. 60: 512-520.
132
Holmes, R.T., and S. K. Robinson. 1981. Tree species preferences of foraging
insectivorous birds in a northern hardwoods forest. Oecologia 48: 31-35.
Holmes, R.T. and J.C. Schultz. 1988. Food availability for forest birds: effects of prey
distribution and abundance on bird foraging. Canadian Journal of Zoology 6: 720728.
Holmes, R.T., T.W. Sherry, P.P. Marra, and K.E. Petit. 1992. Multiple brooding and
productivity of a neotropical migrant, the Black-throated Blue Warbler Dendroica
caerulescens, in an unfragmented temperate forest. Auk 109: 321-333.
Horn, H.S., 1971. The adaptive geometry of trees. Monograph in Population Biology.
Princeton University Press, Princeton, NJ., USA.
Howell, C.A., S.C. Latta, T. M. Donovan, P.A. Porneluzi, G.R. Parks, and John Faaborg.
2000. Landscape effects mediate breeding bird abundance in midwestern forests.
Landscape Ecology. 15: 547-562.
Hutt, S.J., and C. Hutt. 1970. Direct observation and measurement of behaviour. Charles
C. Thomas, Springfield IL.
Hutto, MM.L. 1990. Measuring the availability of food resources. Pages 20-28 in M.L.
Morrison, C.J. Ralph, J. Verner, and J.MM. Jehl Jr., editors. Avian Foraging: Theory,
Methodology and Applications. Studies in Avian Biology No. 13. The Cooper
Ornithological Society. Los Angeles, CA., USA.
James, F.C., and N.O. Wamer. 1982. Relationships between temperate forest bird
communities and vegetation structure. Ecology 63: 159-171.
Jansson, G., and P. Angelstam. 1999. Threshold levels of habitat for the presence of the
Long-tailed tit (Aegithalos caudatus) in a boreal landscape. Landscape Ecology. 14:
283-290.
Jones, J., and R.J. Robertson, 2001. Territory and nest-site selection of cerulean warblers
in eastern Ontario. The Auk. 118: 727-735.
Lambert, D. A., and S.J. Hannon. 2000. Short-term effects of timber harvest on
abundance, territory characteristics, and pairing success of ovenbirds in riparian
buffer strips. The Auk. 117: 687-698.
133
Johnson, D. H. 1980. The comparison of usage and availability measurements for
evaluating resource preference. Ecology 61: 65-71.
Johnson, IM.D., and T.W. Sherry. 2001. Effects of food availability on the distribution of
migratory warblers among habitats in Jamaica. Journal of Animal Ecology 70: 546560.
Karr, J.MM., and MM.MM. Roth. 1971. Vegetation structure and avian diversity in
several New World areas. American Naturalist 105: 423-435.
Kroodsma, MM.L. 1982. Edge effect on breeding forest birds along a power-line
corridor. Journal of Applied Ecology 19: 361-370
Lehner, P. N. 1996. Handbook of ethological methods. Cambridge University Press,
Cambridge, U.K.
Lidicker, W.S. Jr. and W. D. Koenig. 1996. Responses of terrestrial vertebrates to habitat
edges and corridors. Pages 85-109 in D.MM. McCullough, editor. Metapopulations
and wildlife conservation. Island Press, Washington, D.C., USA.
Lima, S.L., and P.A. Zollner. 1996. Towards a behavioural ecology of ecological
landscapes. Tree 11: 131-135.
Litvaitis, J.A, K. Titus, and E.IM. Anderson. 1996. Measuring vertebrate use of terrestrial
habitats and foods. Pages 254-274 in T.A. Bookout, editor. Research and
management techniques for wildlife and habitats. The Wildlife Society, Bethesda,
MD., USA.
Litwin, T.S., and C.MM. Smith. 1992. Factors influencing the decline of Neotropical
migrants in a north eastern forest fragment: Isolation, fragmentation, or mosaic
effects? Pages 483-496 in J.M. Hagan III and D.W. Johnston, editors. Ecology and
conservation of Neotropical migrant landbirds. Smithsonian Institution Press,
Washington, D.C., USA.
Lovette, I.J., and MM.T. Holmes. 1995. Foraging behaviour of American redstarts in
breeding and wintering habitats: implications for food availability. Condor 97: 782791.
Lynch, J.F., and MM.F. Whitcomb. 1978. Effects of insularization of the eastern
deciduous forest on avifaunal diversity and turnover. Pages 461-489 in A.
Marmelstein, editor. Classification, inventory, and analysis of fish and wildlife habitat.
Publication OBS-78716. U.S. Fish and Wildlife Service, Washington, D.C., USA.
MacArthur, MM. H., and John W. MacArthur. 1961. On bird species diversity. Ecology
42: 594-598.
134
MacClintock, L., MM.F. Whitcomb, and B.L. Whitcomb. 1977. Island biogeography and
habitat islands of eastern forest. II. Evidence for the value of corridors and
minimization of isolation in the preservation of biotic diversity. American Birds 31:
6-12.
Majer, J.D., H.F. Recher, W.S. Perriman, and N. Achuthan. 1990. Spatial variation of
invertebrate abundance within the canopies of two Australian eucalypt forests. Pages
65-72 in M.L. Morrison, C.J. Ralph, J. Verner, and J.M. Jehl Jr., editors. Avian
foraging: theory, methodology, and applications. Studies in avian biology no. 13.
Cooper Ornithological Society, Los Angeles, CA., USA.
Matthysen, E. 2002. Boundary effects on dispersal between habitat patches by forest
birds (Parus major, P. caeruleus). Landscape Ecology. 17: 509-515.
Maurer, B.A., and MM.C. Whitmore. 1981. Foraging of five bird species in two forests
with different vegetation structure. Wilson Bulletin 93: 478-490.
Mazzerolle, D.F., and K.A. Hobson. 2001. Physiological ramifications of habitat
selection in territorial male ovenbirds: consequences of landscape fragmentation.
Oecologia 130: 356-363.
McGarigal, K., and W.C. McComb. 1995. Relationships between landscape structure and
breeding birds in the Oregon coast range. Ecological Monographs. 65: 235-260.
McPherson, G. 1990. Statistics in scientific investigation. Springer-Verlag, New York,
NY., USA.
McIntyre, N.E., and J.A. Wiens. 1999. Interactions between landscape structure and
animal behavior: the roles of heterogeneously distributed resources and food
deprivation on movement patterns. Landscape Ecology. 14: 437-447.
Miles, D. 1990. The importance and consequences of temporal variation in avian
foraging behaviour. Pages 210-217 in IM.L. Morrison, C.J. Ralph, J. Verner, and
J.MM. Jehl Jr., editors. Avian foraging: theory, methodology, and applications.
Studies in avian biology no. 13. Cooper Ornithological Society, Los Angeles, CA.,
USA.
Morales, J.M., and S.P. Ellner. 2002. Scaling up animal movements in heterogeneous
landscapes: the importance of behavior. Ecology. 83: 2240-2247.
135
Morrison, M.L., M.W. Mannan, and G.L. Dorsey. 1981. Effects of number of circular
plots on estimates of avian density and species richness. Pages 405-408 in C.J. Ralph
and J.M. Scott, editors. Estimating Numbers of Terrestrial Birds. Studies in Avian
Biology no. 6. Cooper Ornithological Society, Los Angeles, CA., USA.
Morrison, M.L. and E.C. Meslow. 1983. Bird community structure on early-growth
clearcuts in western Oregon. American Midland Naturalist 110: 129-137.
Morrison, M.L., I.C. Timossi, K.A. With, and P.N. Manley. 1985. Use of tree species by
forest birds during winter and summer. Journal of Wildlife Management 49:10981102.
Morse, D.H. 1968. A quantitative study of foraging of male and female sprucewoods warblers. Ecology. 49: 779-784.
Morse, D.H. 1976. Hostile encounters among spruce-woods warblers (Dendroica,
Parulidae). Animal Behaviour 24: 764-771.
Morse, D.H. 1971. The foraging of warblers isolated on small islands. Ecology.
52: 216-228.
Morse, D.H. 1977. The occupation of small islands by passerine birds. Condor 79: 399412.
Morse, D.H. 1978. Structure and foraging patterns of tit flocks in an English woodland.
Ibis 120: 298-312.
Morse, D.H. 1985. Habitat selection in North American Parulid warblers. Pages 131-158
in M.L. Cody editor. Habitat selection in birds. Academic Press. New York, NY.,
USA.
Morse, D.H. 1989. American Warblers. Harvard University Press. Cambridge, MA.
Morse, D.H. 1993. Black-throated green warbler (Dendroica virens). In The
birds of North America, No. 55 (A. Poole and F. Gill, eds.). The Academy of Natural
Sciences, Philadelphia, PA, and the American Ornithologists’ Union, Washington,
D.C., USA.
Mortberg, U.M. 2001. Resident bird species in urban forest remnants: landscape and
habitat perspectives. Landscape Ecology. 16: 193-203.
136
Norse, E.A., K.L. Rosenbaum, D.S. Wilcove, B.A. Wilcox, W.H. Romme, IM.W.
Johnston, and IM.L. Stout. 1986. Conserving biological diversity in our national
forests. The Wilderness Society, Washington, D.C., USA.
Orians, G.H. 1991. Supplement: Habitat Selection. American Naturalist.
137: 51-54.
Parrish, J. D. 1995a. Effects of needle architecture on warbler habitat selection in
a coastal spruce forest. Ecology. 76. 1813-1820.
Parrish, J.D. 1995b. Experimental evidence for intrinsic microhabitat preferences
in the black-throated green warbler. Condor. 97: 935-943.
Penhollow, M.E., and D.F. Stauffer. 2000. Large-scale habitat relationships of
neotropical migratory birds in Virginia. Journal of Wildlife Management. 64: 362373.
Pettersson, R.B., J.P. Ball, K-E Renhorn, P-A. Esseen, and K. Sjoberg. 1995. Invertebrate
communities in boreal forest canopies as influenced by forestry and lichens with
implications for passerine birds. Biological Conservation. 74: 56-63.
Porneluzi, P., J.C. Bednarz, L.J. Goodrich, N. Zawada, and J. Hoover. 1993.
Reproductive performance of territorial Ovenbirds occupying forest fragments and a
contiguous forest in Pennsylvania. Conservation Biology 7: 618-622.
Remsen, J. V., and S. K. Robinson. 1990. A classification scheme for foraging behaviour
of birds in terrestrial habitats. Pages 144-160 in M.L. Morrison, C.J. Ralph, J.
Verner, and J.M. Jehl Jr., editors. Avian Foraging: Theory, Methodology and
Applications. Studies in Avian Biology No. 13. Cooper Ornithological Society, Los
Angeles, CA., USA.
Rice, J., M.D. Ohmart, and D.W. Anderson. 1983. Habitat selection attributes of an avian
community: a discriminant analysis investigation. Ecological Monographs 53: 263290.
Robbins, C.S., D.K. Dawson, and B. Hoover. 1989. Habitat area requirements of
breeding forest birds of the middle Atlantic states. Wildlife Monographs 103: 1-34.
Robichaud, I., and M.-A. Villard. 1999. Do Black-throated Green Warblers prefer
conifers? Meso- and microhabitat use in a mixed wood forest. Condor 101: 262-271.
Robichaud, I., M-A Villard, and C.S. Machtans. 2002. Effects of forest regeneration on
songbird movements in a managed forest landscape of Alberta, Canada. Landscape
Ecology. 17: 247-262.
137
Robinson, S.K., and R.T. Holmes. 1982. Foraging behaviour of forest birds: the
relationships among search tactics, diet, and habitat structure. Ecology 63: 19181931.
Robinson, S.K., and R.T. Holmes. 1984. Effects of plant species and foliage structure on
the foraging behaviour of forest birds. Auk 101: 672-684.
Robinson, S.K., M.M. Thompson III, T.M. Donovan, D.M. Whitehead, and J. Faaborg.
1995. Regional forest fragmentation and the nesting success of migratory birds.
Science 267: 1987-1990.
Roland, J., and P. P. Taylor. 1997. Insect parasitoid species response to forest structure at
different spatial scales. Nature 386: 710-713.
Rosenberg, K.V. and M.J. Cooper. 1990. Approaches to avian diet analysis. Pages 80-90
in M.L. Morrison, C.J. Ralph, J. Verner, and J.M. Jehl Jr., editors. Avian foraging:
theory, methodology, and applications. Studies in avian biology no. 13. Cooper
Ornithological Society, Los Angeles, CA., USA.
Sheskin, D.J. 1997. Handbook of parametric and nonparametric statistical procedures.
CRC Press, Boston, MA., USA.
Sherry, T.W., and MM.T. Holmes. 1985. Dispersion patterns and habitat responses of
birds in northern hardwoods forests. Pages 283-309 in M.L. Cody editor. Habitat
selection in birds. Academic Press. New York, NY., USA.
Sherry, T.W., and R.T. Holmes. 1997. American redstart (Setophaga ruticilla). In The
birds of North America, No. 277 (A. Poole and F. Gill, eds.). The Academy of Natural
Sciences, Philadelphia, PA, and the American Ornithologists’ Union, Washington,
D.C., USA.
Slater, P.J.B. 1978. Data collection. Pages 7-24 in P. Colgan, editor. Quantitative
ecology. John Wiley and Sons, New York, NY., USA.
South, A.B., S.P. Rushton, R. E. Kenward, and D.W. Macdonald. 2001.
Modelling vertebrate dispersal and demography in real landscapes: how does
uncertainty regarding dispersal behaviour influence predictions of spatial
population dynamics? Pages 327-349 in J.M. Bullock, R.E. Kenward, and
R.S. Hails, editors. Dispersal Ecology. The 42nd Symposium of the British
Ecological Society, 2001. Blackwell Publishing, Oxford, UK.
138
Spies, T.A., W.J. Ripple, and G.A. Bradshaw. 1994. Dynamics and pattern of a managed
coniferous forest landscape in Oregon. Ecological Applications 4: 555-568.
Strong, A. 2000. Divergent foraging stategies of two neotropical migrant warblers:
implications for winter habitat use. The Auk. 117: 381-392.
Taylor, J.A., G.MM. Friend, and M.L. Dudzinski. 1984. Influence of sampling strategy
on the relationship between fauna and vegetation structure , plant life form and
floristics. Australian Journal of Ecology 9: 281-287.
Urban, D.L., H.H. Shugart Jr., D.L. DeAngelis, and M.V. O’Neil. 1988. Forest bird
demography in a landscape mosaic. Publication no. 2853. Oak Ridge National
Laboratory, Oak Ridge, TN., USA.
Villard, M.A., K. Freemark and G. Merriam. 1992. Metapopulation theory and
Neotropical migrant birds in temperate forests: an empirical investigation. Pages 474482 in J.M. Hagan III and D.W. Johnston, editors. Ecology and conservation of
Neotropical migrant landbirds. Smithsonian Institution Press, Washington, D.C.,
USA.
Villard, M.-A., P.M. Martin, and C.G. Drummond. 1993. Habitat fragmentation and
pairing success in the Ovenbird (Seiurus aurocapillus). Auk 110: 759-768.
Virkkala, R. 1988. Foraging niches of foliage-gleaners in northern Finland. Ornis
Fennica. 65: 104-113.
Wahlter, B.A. 2002. Grounded ground birds and surfing canopy birds: variation of
foraging stratum breadth observed in neotropical forest birds and tested with
simulation models using boundary constraints. The Auk. 119: 658-675.
Whelan, C.J. 1989a. Avian structure preferences for foraging and the effect of
prey biomass. Animal Behaviour. 38: 839-846.
Whelan, C.J. 1989b. An experimental test of prey distribution learning in two paruline
warblers. Condor. 91: 113-119.
139
Whelan, C.J. 2001. Foliage structure influences foraging of insectivorous forest birds: an
experimental study. Ecology 82: 219-231.
Wiens, J.A. 1989. The Ecology of Bird Communities, Volume 1. Cambridge University
Press, New York, NY., USA.
Wiens, J.A. 1995. Landscape mosaics and ecological theory. Pages 1-26 in L. Hansson,
L. Fahrig, and G. Merriam, editors. Mosaic Landscapes and Ecological Processes.
Chapman and Hall, New York, NY., USA.
Wiens, J.A. 1996. Wildlife in patchy environments: Metapopulations, mosaics, and
management. Pages 53-84 in D.MM. McCullough, editor. Metapopulations and
wildlife conservation. Island Press, Washington, D.C., USA.
Wilcove, D.S. 1985. Nest predation on forest tracts and the decline of migratory
songbirds. Ecology 66: 12111-1214.
Willson, IM.F., and T.A. Comet. 1996. Bird communities of northern forests: patterns of
diversity and abundance. Condor 98: 337-349.
Willson, IM.F. 1974. Avian community organization and habitat structure. Ecology 55:
1017-1029.
Wolda, H. 1990. Pages 38-43 in M.L. Morrison, C.J. Ralph, J. Verner, and J.M. Jehl Jr.,
editors. Avian Foraging: Theory, Methodology and Applications. Studies in Avian
Biology No. 13. Cooper Ornithological Society, Los Angeles, CA., USA.
Wolter, P.T., and M.A. White. 2002. Recent cover type transitions and landscape
structural changes in northeast Minnesota, USA. Landscape Ecology. 17: 133-155.
Wu, J., and R. Hobbs. 2002. Key issues and research priorities in landscape ecology: An
idiosyncratic synthesis. Landscape Ecology. 17: 355-365.
Zannette, L., P. Doyle, and S. IM. Tremont. 2002. Food shortage in small fragments:
evidence from an area-sensitive passerine. Ecology 81: 1654-1666.
Zar, J. H. 1996. Biostatistical analysis. Prentice Hall, Upper Saddle River, NJ.,USA.
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Vita
Peter S. McKinley
Professional Experience
1999-Present (concurrent with Ph.D. program), Hancock Land Company, Casco, ME.,
USA. Vice President of Operations and Chief Ecologist.
1992-1995, Manomet Center for Conservation Sciences, Manomet, MA., and Brunswick,
ME., USA. Full time Project Manager and Biologist.
Summer 1991, Indiana University, Bloomington, IN., USA. Field Research Manager.
Summer of 1988, Concord Conservation Commission, Concord NH., USA. Conservation
Intern.
Education and School Related Experience
1996-Present, University of New Brunswick, Fredericton, NB, CA. Ph.D. student
in Department of Biology.
1988-1991, Indiana University, Bloomington, IN., USA.
M.S. Applied Ecology/Environmental Science.
1983-1987, Colby College, Waterville, ME., USA. B.A. Biology.
Publications
Hagan, J.M., M.W. Vander Haegen, and P.S. McKinley. 1996. The early development
of forest fragmentation effects on birds. Conserv. Biol. 10: 188-202.
Hagan, J.M., P.S. McKinley, A.L. Meehan, and S.L. Grove. 1997. Diversity and
abundance of birds in a north eastern industrial forest. J. Wildl. Manage. 61: 718-735.
McKinley, P.M. 1999. Songbird foraging success in two co-dominant hardwood tree
species in a managed mixed-wood forest. Proceedings of The Sustainable Forest
Management Network Conference. 69-73. Universtiy of Alberta, Edmunton, AB., CA.
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