Downy Woodpecker
Habitat Suitability in
Gourdneck State Game
Area, Michigan
Emma Fojtik
Western Michigan University
Kalamazoo, MI 49008
E-mail: [email protected]
Lisa M. DeChano-Cook *
Western Michigan University
Kalamazoo, MI 49008
E-mail: [email protected]
ABSTRACT
This study examines the habitat suitability
for the downy woodpecker (Picoides pubescens) for a parcel of land in Gourdneck State
Game Area (GSGA), Kalamazoo County,
Michigan. Land within GSGA has undergone
habitat restoration from forest and shrub to
savanna and prairie, intentionally excluding
two parcels. This study took place on one of
the excluded parcels. We used the Habitat
Suitability Index Model created by the Fish
and Wildlife Service to determine suitability.
We measured basal area and number of snags
in 0.4 hectares to determine the food and
reproduction life requisites that are the basis
of the Habitat Suitability Index Model for
the downy woodpecker. Results revealed that
the study site is ideal for the reproduction life
requisite but the food life requisite could be
improved with habitat management. While
the study site is not optimal for both variables, we suggest that management could cull
some snags that would make this site more
suitable for the downy woodpecker.
Key Words: downy woodpecker (Picoides
pubescens), Gourdneck State Game Area,
Habitat Suitability Index
INTRODUCTION
* Corresponding Author
The Geographical Bulletin 57: 15-23
©2016 by Gamma Theta Upsilon
Over the span of many decades, landscape
change throughout the United States has
thoroughly altered the spatial habitats of
many different species. Some species respond
to these changes by seeking other suitable
lands for food, shelter, and reproduction.
However, species do not possess such capabilities. In some cases, landscape modifications lead to a decrease of a species, leading to
population increases for other species, which
could then cause potentially increased stress
on the ecosystem. For example, the loss of a
predator population such as wolves (Canis
lupus) or coyotes (Canis latrans) results in
increases in other species populations such as
white-tailed deer (Odocoileus virginianus) or
15
Emma Fojtik and Lisa M. DeChano-Cook
eastern cottontail rabbits (Sylvilagus floridanus). These increases in population can stress
the ecosystem because diversity is further
reduced (Prugh et al. 2009; Hebblewhite
et al. 2005; Berger et al. 2001; Crooks and
Soule 1999).
When habitats are restored, this can have
positive effects for some species but negative
influences on others. For instance, Gourdneck
State Game Area (GSGA) in Kalamazoo County, Michigan, has been a habitat restoration site
for many years. A planned initiative to revert
the forested area of the largest parcel into prairie
and savanna is being carried out to create habitats that are more suitable for certain species
such as wild turkey (Meleagris gallopavo) and
cottontail rabbits. However, there is evidence
that suggests changes resulting from such restoration effectors may be disadvantageous for
other species, such as the downy woodpecker
(Picoides pubescens). The impact on this species
is the focus of the current study.
General models for habitat suitability for
individual species have been developed by the
U.S. Fish and Wildlife Service (Schamberger,
Farmer, and Terrell 1982). Based on basic
species requirements, a Habitat Suitability
Index (HSI) has been constructed for individual species. Such models take into account
habitat use for factors such as food, water,
cover and reproduction requirements when
determining suitable habitats for avian species. The HSI for the downy woodpecker
(Schroeder 1983) includes two basic habitat
variables – basal area of trees and number of
snags. Basal area governs the suitability of
the study site for the food life requisite while
the number of snags determines the parcel’s
suitability for the reproduction life requisite
of this species.
There are three other smaller plots within
GSGA not included in the habitat restoration that have land covers conducive to the
downy woodpecker, namely deciduous forest, riparian areas and open areas with little
coniferous forest (Jackson and Ouellet 2002).
We examined one of these smaller parcels to
evaluate its suitability as downy woodpecker
habitat based on the HSI for that species.
16
THE DOWNY WOODPECKER
Habitat
With the exception of parts of Texas and
the arid southwest (McCommons 2002),
downy woodpeckers inhabit virtually the
entirety of North American where trees and
forests can be found (Jackson and Ouellet
2002). Measuring 14.5 to 17 centimeters
long and weighing 20 to 28 grams, the
downy woodpecker is the smallest of all the
native woodpecker species in North America
(Kirschbaum 2005) (Fig. 1).
Beal described the downy woodpecker
as “one of our most useful species” (1911,
22). Many birds, not just woodpeckers, consume harmful invasive species, often in large
quantities. However, the rate at which downy
woodpeckers consume destructive larvae is
effective in controlling insects considered to
be pests (Bruns 1960; Beal 1911). For example, the woodpecker is a known predator
of the emerald ash borer (Agrilus planipennis),
an invasive beetle that can cause detrimental damage to ash trees (Lindell et al. 2008).
When studied, a positive correlation was
found between woodpecker predation levels
and density of EAB in a tree, with the downy
woodpecker spending much of its time in
ash trees (Lindell et al. 2008). According
to Beal (1911), the downy woodpeckers’
food selection consisted almost entirely of
economically harmful species.
Figure 1. Downy woodpecker. Source: Elder
2015.
Downy Woodpecker Habitat Suitability in Gourdneck State Game Area, Michigan
Another benefit of a strong downy woodpecker population is that downy woodpeckers usually excavate a new nest cavity
each year, leaving their old nest cavities for
secondary cavity nesters, or those who do
not excavate their own nests. “It is well-know
that woodpeckers provide cavities for secondary cavity-nesters” (Virkkala 2008, 82).
The downy woodpecker provides secondary
cavities for red-breasted nuthatches (Sitta
canadensis), which are found to increase their
population in areas following a year of downy
woodpeckers nesting in the area (Norris and
Martin 2010).
Foraging Needs
Beal (1911) examined the stomachs of
723 downy woodpeckers to understand
their diets. He concluded that 76.05% of
their diet consisted of animal foods, such as
beetles, caterpillars, ants, while the remaining
23.95% of their diets consisted of vegetable
matter, such as seeds and fruit. The foraging
behavior of the downy woodpecker generally varies with efficiency of acquiring food,
meaning the bird will use the most efficient
method to maximize return on the foraging
investment. There are four foraging behaviors
used by the downy woodpecker: percussion,
scaling, peering and poking, and flycatching (Jackson 1970). Percussion refers to
the “rapid continuous series of blows” the
woodpecker produces on a limb, digging out
its prey once found. Scaling occurs when the
woodpecker moves up and down a tree or
trunk, stopping if food presents itself. Peering and poking is self-descriptive, in that the
woodpecker utilizes its known senses to find
its prey. Flycatching, the most infrequent of
all the methods, is usually observed when
gatherings of insects occur around sap coming from the tree. Williams (1975) found in
a study of the central forests of Illinois that
downy woodpeckers generally forage more
in lower areas of trees, as oppose to high
in the tree canopies. It was also noted that
downy woodpeckers foraged more often on
live limbs rather than dead limbs.
Schroeder (1983) determined that downy
woodpeckers foraging needs are met when
basal areas of trees measure between 10 and
20 m2/ha. Although 10 to 20 m2/ha is ideal
for foraging needs of the downy woodpecker,
the species is still capable of finding food in
areas where the basal area is greater than 20
m2/ha.
Reproductive Needs
The importance of nesting for a downy
woodpecker is directly related to their ability
to reproduce, meaning without a nest/cavity, the downy woodpecker has no means of
reproduction (Kirschbaum 2005; Schroeder
1983). Because it breeds yearly, each year the
downy woodpecker must either find a cavity
that is new to it to nest in or excavate another
(Kirschbaum 2005).
Evans and Conner (1979) state the downy
woodpecker is a dominant cavity nester, preferring soft snags for nesting sites, such as
those found in deciduous forest, evergreen
forest and forested wetlands (Kirschbaum
2005; Schroeder 1983). Generally, dead or
dying wood is necessary for the woodpecker
to be successful in creation of the cavity
(Kirschbaum 2005; Schroeder 1983). The
male and female excavate a nest together, on
average 15.3 meters above ground (Schroeder
1983), with excavation taking anywhere from
seven to ten days (Kirschbaum 2005). The
Habitat Suitability Index (HSI) being used in
this research states that downy woodpeckers
require nesting trees to have diseases, including sap rot and heart rot, which softens the
outside and inside of the tree for more efficient cavity excavation (Schroeder 1983).
Kilham (1974) states downy woodpeckers
seem to have an image of an optimal nest site,
preferring live trees with dead, broken-off
tops. A photograph of four snags with broken
of tops at the study site can be seen in Fig. 2.
A photograph of a snag with woodpecker evidence from the study site can be seen in Fig.
3. Ideal nest sites for downy woodpeckers are
mostly in short supply, consequently limiting
where downy woodpeckers can live (Schro17
Emma Fojtik and Lisa M. DeChano-Cook
Figure 2. Four snags at study site. Source:
Authors.
Figure 3. Snag with evidence of woodpecker
activities at study sites. Source: Authors.
eder 1983). Through estimation, Evans and
Conner (1979) were able to determine that
downy woodpeckers present in northeastern
areas of North America require roughly 9.9
snags with a diameter at breast height (DBH)
ranging from 15 to 25 centimeters per hectare, or about four snags per acre. The optimal
habitat of the downy woodpecker is 12.4
snags per hectare (Schroeder 1983; Evans
and Conner 1979). For the purpose of this
study, the Habitat Suitability Index Model’s
reproduction component of five snags per
acre is used to determine the suitability of the
downy woodpeckers reproduction resources.
original prairie and savanna landscape lost
due to agriculture since the 1830s (Chapman
and Brewer 2008). Management personnel
intentionally omitted two smaller parcels
of land in Sections 19 and 20 in order to
evaluate each parcel’s viability to serve the
purpose for which they were originally purchased (Crane Pond Field Office 2005). The
smaller parcel in Section 20 is the study site
for this research.
The study site itself is roughly 77 hectares,
holding a mixture of deciduous and coniferous trees. The northeastern area of the study
site contains deciduous forest species such
as maple (Acer spp.), American beech (Fagus
grandifolia), and black cherry (Prunus serotina), while woodland in the northwest and
central portions of the parcel is composed
primarily of eastern white pine forests (Pinus
strobus). The southern area of the study site
consists of a more mature deciduous forest,
which tapers into a deciduous wetland area
in the lower southwestern corner of the study
site.
STUDY SITE
Gourdneck State Game Area (GSGA) is
located in south-central Kalamazoo County,
and lies in portions of sections 19, 20, 2932 of Township 3 South, Range 11 West,
and sections 3, 4, 9, and 10 of Township 4
South, Range 11 West (Fig. 4). Sections 30
and 31 are undergoing a habitat restoration
project from secondary forest back to its
18
Downy Woodpecker Habitat Suitability in Gourdneck State Game Area, Michigan
Figure 4. Map of Gourdneck State Game Area, with the study area highlighted in the upper
left (2006)
19
Emma Fojtik and Lisa M. DeChano-Cook
HABITAT SUITABILITY INDEX MODEL
(HSI)
Schroeder, funded by the US Department
of Interior’s Fish and Wildlife Service, developed the HSI for the downy woodpecker
which was published in 1983. The model
uses two variables to determine habitat suitability, basal area and number of snags, each
within 0.4ha. Basal area is important for food
for the downy woodpecker, while the number
of snags is important for their reproduction.
Basal area is optimal if it is between 10 and
20 m2/hectare (ha). We determined basal area
by measuring the diameter of each tree at
breast height (dbh; 1.4m above the ground)
within ten 0.04ha plots. The second variable
is number of snags within a 0.4ha parcel.
Schroeder (1983, 7) defines snags as “trees
in which at least 50% of the branches have
fallen, or are present but no longer bear foliage.” Snags must be larger than 15cm dbh to
be suitable for the downy woodpecker to use
it for cavity excavation. The HSI also requires
that a minimum of 4ha of potentially useable
habitat be present or the HSI will equal zero
(Schroeder 1983). In this case, the study site
measures about 77ha, allowing for plenty of
potentially useable habitat throughout the
study site.
tree within the circle had its dbh measured
and recorded. We also recorded whether each
tree met Schroeder’s definition of a snag.
DATA ANALYSIS
We converted all tree dbh measurements
into basal areas using equation below.
Basal area (m2) = 0.00007854 x dbh2
After all tree basal areas were calculated,
we summed the basal areas of each sample
plot and for the total 0.4ha study site. This
total basal area was then compared with the
HSI’s basal area graph (Fig. 5) to determine
suitability. We summed the number of snags
for each sample plot and the total 0.4ha plot
and compared the total number of snags to
the HSI graph for this variable (Fig. 6) to
determine the suitability of the reproduction
life requisite.
RESULTS AND DISCUSSION
Table 1 displays the total basal area and
number snags for each of the 10 sample plots
as well as the total basal area and number of
snags for the study site. The total basal for our
study site was 31.03 m2/ha. Based on Figure
FIELD DATA COLLECTION
20
0.8
Suitability index
For proper use of HSI 0.4ha needs to be
measured. We measured ten 0.04ha round
plots distributed randomly throughout the
study parcel, as suggested by Washington
State University Extension (2015). To obtain
our sample plots we created a map of the
study site in ArcMap 10.1 (ESRI 2011). We
then employed the random sampling tool
to find points in the study site. The first 10
points were used as center points for our onetenth acre plots. We reserved the last point in
case one of the other points was inaccessible.
We used a GPS to find each plot’s center
point and drove a stake into the ground. A
rope of 11.3m was then attached to the stake
to determine the boundary of the plot. Every
1.0
0.6
0.4
0.2
0.0
0
10
20
30+
Basal area (m /ha)
2
Figure 5. Basal area diagram used to determine suitability, Schroeder 1982.
Downy Woodpecker Habitat Suitability in Gourdneck State Game Area, Michigan
1.0
Suitability index
0.8
0.6
0.4
0.2
0.0
0
1
2
3
4
5+
Snags (number/0.4 ha)
Figure 6. Number of snags diagram for determining suitability, Schroeder 1982.
5 this area exhibits a 50% suitability for the
food life requisite as it exceeds the value of
30m2/ha on the graph. While this is not the
optimal condition, it does have some value.
Schroeder (1983, 5) stated “stands with basal
areas greater than 30m2/ha, or about 50%
suitability, are assumed to have moderate
value for downy woodpeckers.”
Table 1. Total basal area and number of snags
for each sample plot in the study area.
Plot
Total Basal Area
(m2/0.04ha)
Total Number
of Snags
1
5.93
0
2
21.87
2
3
15.35
3
4
6.01
0
5
23.10
0
6
9.18
1
7
13.55
5
8
13.67
2
9
10.31
1
10
16.51
2
Total
135.48m2/0.4ha
16
The total number of snags for this study
site was 16 snags/0.4ha. A comparison of
our results to Figure 6 indicates that the reproduction life requisite is optimal based on
Evans and Conner’s (1979) and Schroeder’s
(1983) assertion that at least 12.4 snags per
hectare is optimal.
Our original hypothesis stated that we
believed our sample plot was 100% for
the downy woodpecker for both basal area
and number of snags. While the number
of snags was optimal for the reproduction
life requisite, the total basal area was much
larger than optimal (only 50% suitable) for
the food life requisite we cannot accept our
hypothesis. However, this does not mean
that this site does not hold any value. Downy
woodpeckers can still inhabit this area but a
large population of this species is not viable
unless something is done to create a more
optimal habitat.
If management personnel at GSGA want
to create a prime habitat for both the food
and reproduction life requisites the basal area
would need to be decreased by approximately
35%. In order to accomplish this, GSGA
forest management practices need to be
reviewed. In regards to basal area, northern
hardwood forests such as those in Michigan
grow at their best when basal area is between
69 and 89 m2/acre (Neumann 2001). This
ideal basal area is consistent with the habitat
suitability needs of the downy woodpecker.
Neumann (2001) suggests that stands with
basal areas greater than 99 m2/ha or more be
thinned so that tree growth and health do not
decline. If thinning was to occur in our plot,
management personnel would need to keep
in mind that the downy woodpecker does
required some dead or diseased trees for cavity excavation (Kirshbaum 2005; Neumann
2001; Schroeder 1983). Keeping in mind
that the optimal habitat requires at least five
snags per 0.4ha, no more than 11 snags can
be removed from the study site.
To achieve 100% habitat suitability for the
downy woodpecker in terms of both basal
area and number of snags, a thinning initiative would require proper planning. Manage21
Emma Fojtik and Lisa M. DeChano-Cook
ment personnel could remove some of the
bigger trees with large basal areas. Based on
our estimates of basal area and number of
snags, removal of five of the 15 largest snags
and ten of the largest non-snags from our
sample plot would produce a total basal area
of 18.4m2/ha. This site would then fall within
the optimal range for both basal areas and
number of snags. While this is a temporary
solution, if this method of forest management was implemented over the course of
several years, the suitability may become
consistent at 100% suitability.
CONCLUSIONS
Due to extensive urbanization and sprawl,
many species’ habitats are decreasing or even
disappearing. Some of these species do not
have the adaptive capacity to survive; however, some do. The downy woodpecker is one
such species that has the ability to occupy
spaces that have been heavily influenced by
humans (Jackson and Ouellett 2002).
Gourdneck State Game Area (GSGA) in
southcentral Kalamazoo County has endured
human modification, as it is not one contiguous parcel of land but several small plots.
We examined one of these parcels for downy
woodpecker habitat suitability. We found
that the study site had a greater basal area
of trees than is considered ideal, while the
number of snags was optimal for the downy
woodpecker. A modification to the study site
of removing some of the larger trees and some
of the larger snags would bring both measurements to optimal values. This would make
this plot in the Gourdneck State Game Area
a desirable site for the food and life requisites
of the downy woodpecker.
There may also be other areas of this state
game area that are suitable for the downy
woodpecker, such as the wetland area just
west of the current study site which appears
to have a smaller total basal area than out
study site. Because deciduous wetlands
are capable of supporting suitable downy
woodpecker habitat, it would be reasonable
to expand our study to the neighboring wet22
land parcel to determine its suitability for the
downy woodpecker.
ACKNOWLEDGEMENTS
We would like to thank Lucius Hallett
for his guidance throughout this project
and for his critical review of a draft of this
manuscript. We would also like to thank the
anonymous reviewer for the time spent providing suggestions to make this manuscript
stronger. We are very grateful to this person.
REFERENCES
Beal, F. 1911. Food of the Woodpeckers
of the United States. U.S. Department
of Agriculture, Biological Survey Bulletin,
37:1-64.
Bent, A. C. 1939. Life Histories of North
American woodpeckers. United States National Museum Bulletin, 174:334.
Berger, J., Stacey, P. B., Bellis, L, and Johnson,
M. P. 2001. A Mammalian Predator-Prey
Imbalance: Grizzly Bear and Wolf Extinction Affect Avian Neotropical Migrants.
Ecological Applications, 11:947-960.
Bruns, H. 1960. The Economic Importance
of Birds in Forests. Bird Study, 7:193-208.
Chapman, K. A. and Brewer, R. 2008. Prairie
and Savanna in Southern Lower Michigan:
History, Classification, Ecology. Michigan
Botanist, 47:1-48.
Crane Pond Field Office. 2005. Master Plan
for Gourdneck State Game Area (draft).
Michigan Department of Natural Resources, Wildlife Division.
Crooks, K. R., and Soule, M. E. 1999.
Mesopredator Release and Avifuaunla Extinctions in a Fragmented System. Nature,
400:563-566.
Elder, W. 2015. Photos of Downy Woodpecker. [http://www.nps.gov/prsf/learn/
nature/downy-woodpecker.htm]. Last
accessed on May 23, 2015.
Evans, K. E., and Conner, R. N. 1979. Snag
management. Forest Service General Technical Report No. NC-51.U.S. Department
of Agriculture.
Downy Woodpecker Habitat Suitability in Gourdneck State Game Area, Michigan
Hebblewhite, M., White, C. A., Nietvelt, C.
G., McKenzie, J. A., T. E., Fryxell, J. M,
Bayley, S. E., and Paquet, P. C.. 2005. Human Activity Mediates a Tropical Cascade
Caused by Wolves. Ecology, 86:2135-2144.
Jackson, J., and Ouellet H. 2002. Downy
woodpecker (Picoides pubescens). In A
Poole, F Gill, eds. The Birds of North
America, Vol. 613. Philadelphia, PA: The
Birds of North America, Inc. Pp. 1-32
Kirschbaum, K. 2005. Picoides pubescens.
[http://animaldiversity.ummz.umich.
edu/accounts/Picoides_pubescens/]. Last
accessed on March 15, 2015.
Lindell, C. A., McCullough, D. G., Capparet, D., Apostolou, N. M., and Roth, M.
B. 2008. Factors Influencing Woodpecker
Predation on Emerald Ash Borer. American
Midland Naturalist, 159:434-444.
McCommons, J. 2002. The Downy Woodpecker. Organic Gardening, 49:20.
Norris, A. R., and Martin, K. 2010. The
Perils of Plasticity: Dual Resource Pulses
Increase Facilitation but Destabilize Populations of Small-Bodied Cavity-Nesters.
Oikos, 119:1126-1135.
Prugh, L, R, Stoner, C. J., Epps, C. W., Bean,
W. T., Ripple, W. J., Laliberte, A. S., and
Brashares, J. S. 2009. The Rise of the Mesopredator. BioScience, 5:779-790.
Schamberger, M. A., Farmer, A. H., and
Terrell, J. W. 1982. Habitat Suitability
Index Models : Introduction. U.S.D.I. Fish
and Wildlife Service. FWS/OBS-82/10.
2 pp.
Schroeder, R. L. 1982. Habitat Suitability Index Models: Downy woodpecker. No.
FWS/OBS-82/10.38. U.S. Department of
Interior, Fish and Wildlife Service.
Virkkala, R. 2006. Why Study Woodpeckers?
The Significance of Woodpeckers in Forest Ecosystems. Annales Zoologici Fennici,
43:85.
Washington State University Extension. 2015
Virtual Cruisers Vest, lesson 4: Establishing Fixed Plots. [http://forestandrange.
org/Virtual%20Cruiser%20Vest/lessons/
lesson_04/Lesson_4_PDF.pdf ]. Last accessed on May 25, 2015.
Williams, J. B. 1975. Habitat Utilization by
Four Species of Woodpeckers in a Central
Illinois Woodland. American Midland
Naturalist, 93:354-367.
23
24