© Biodiversity Heritage Library, http://www.biodiversitylibrary.org/
Z. Säugetierkunde 54 (1989) 107-110
©
1989 Verlag Paul Parey,
Hamburg und
Berlin
ISSN 0044-3468
Comparative food habits of three carnivores
Western Sierra Madre, Mexico
By M. Delibes, Lucina Hernandez and
Estacion Biolögica de
F.
in
Hiraldo
Sevilla, Spain, Instituto de Ecologia, Mexico D.F., Mexico and Museo
Nacional de Ciencias Naturales, Madrid, Spain
Donana,
Receipt of Ms. 22. 10. 1987
Abstract
Studied are the foods
and
diet
partitioning
of coyotes
(Canis latrans),
gray foxes
(Urocyon
on the Western Sierra Madre, Mexico, during summer
1981 and spring 1982. The three carnivores were generalist feeders, but coyotes ate mainly rodents,
gray foxes fruit, and coatis arthropods. Trophic diversity and mean prey size were largest in the
coyote, intermediate in the gray fox, and smallest in the coati. The least dietary overlap occurred
between the coyote and the coati. Because prey abundance was the same for the 3 species, differences
were assumed to reflect different feeding, behaviour and ecology.
cinereoargenteus), and coatis (Nasua narica)
Introduction
The
natural history of North American carnivores south of the United States is poorly
documented. Information on the ecology of Mexican mammalian predators is limited, and
most of the available data concern coyote-livestock problems in cattle ranges of Chihuahua
(e.g. Perez-Gutierrez et al. 1982; Lafon 1983). The objectives of our study were to
examine spring and summer food habits of coyotes {Canis latrans), gray foxes {Urocyon
cinereoargenteus), and coatis (Nasua narica) in the oak-pine woodlands of the Western
Sierra Madre and to compare the food-resource partitioning among these sympatric
carnivores.
Study area
The study was done
Biosphere Reserv^e of La Michilia, in the Mexican State of Durango
(approx. 23°27'N, 104°18'W). Located in a transition zone ranging from high mountains to plateaus,
the reserve has an average altitude of 2250
and is an irregulär high piain between 2 mountain ranges,
the Sierras of Urica and Michis. Climate is semiarid temperate with summer rains (600
per year)
and annual mean temperature of 19 °C (Gallina 1981). Vegetation is dominated by oak-pine forests
{Quercus sp., Pinns sp.) with local patches of juniper {Juniperus sp.), manzanita thickets (Arctostaphylos sp.) and open grasslands. Besides the 3 carnivore species studied, mountain lions (Felis concolor),
bobcats (Felis rufus), raccoons (Procyon lotor), ringtails (Bassariscus astutus), long-tailand weasels
(Mustela frenata), and 2 skunks (Mephitis macroura, Conepatus mesoleucus) also have been recorded
in the area. Occasional wolf (Canis lupus) observations are recorded, and black bears (Ursus
americanus) apparently were extirpated several years ago.
in the
m
mm
Material and methods
We
collected 116 coyote, 99 gray fox and 87 coati faeces along dirt roads and paths of the reserve
during July-August 1981 and April 1982. Faeces were identified to species based upon size, shape and
odour (MuRiE 1974). We discarded very old faeces and those that could not be identified. Identification of prey items was made by comparison with a reference coUection of hairs, teeth, seeds, etc.
Occasional grasses and twigs occurring in faeces were not considered in the analysis. Mammal remains
were identified to species when possible. We could not distinguish whether ungulates were killed by
predators or consumed as Carrion.
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M.
108
Hernandez and
Delihes, Lucina
Hiraldo
F.
For each species, food items were quantified as: 1. number of occurrences (N), Ni = number of
where the i category of remains occurs, and 2. proportion of occurrence (PO), POi = number of
faeces where the i category of remains occurs x 100/number of total occurrences of all categories in all
examined faeces. This method does not reflect precisely the weight of ingested material, but indicates
the relative role of the various items in the diet (Erlinge 1968).
We used G test (Sokal and Rohlf 1981) to compare the distribution pattern of each prey category
in the diet of the 3 predators. When significant differences were found for 1 category, the observed
frequency in each diet of this category was compared with the expected frequency under the null
faeces
i.e., the prey category is equally frequent in the faeces of all 3 predators.
Trophic diversity (food-niche breadth) that measures the width of prey-use categories was
estimated as (Levins 1968):
hypothesis,
B =
where B
1/2
pi^
food-niche breadth, and Pi is the relative occurrence of prey category i in the diet of a given
species. This expression generates values from 1 to the number of used categories, 7 in this instance.
Trophic similarity (food-niche overlap) of 2 species that measures the shared parts of their trophic
niches was estimated as (Pianka 1973):
is
A
A is food-niche overlap,
where
species
p and
q.
and
= 2piqi/(2pi22qi2)i/2
and
qi are the relative occurrences of category i in the diet of the
This expression renders values ranging from 0, no overlap, to 1, complete overlap.
p;
Results and discussion
The
carnivores were generalists. Ungulates, rabbits, rodents, reptiles, invertebrates,
3
all were found in the faeces we examined (Table 1). However, the major
food items in the pooled faeces of the 3 species were fruit and berries (33.5 %), arthropods
fruits,
Table
and berries
1.
Food
Spring and
categories
Ungulates
Rabbits
Rodents
Birds
Reptiles
Arthropods
Fruit and berries
Trophic diversity
summer
diet of coyotes, gray foxes and coatis in the Western Sierra Madre,
Mexico, based on the analysis of faeces (n)
Coyote
=
(n
116)
Gray fox
(n
99)
Coati (n = 87)
P<
PO
19
10.6 (+)
7.2 (+)
2
1.2
1
0.7
23.21
0.001
2
1.2
1
0.7
13.34
O.Ol
35.0 (+)
37
21.5
9
6.7 (-)
31.60
0.001
7
4.1
2
1.5
63
6
4
39
36
3.3
2.2
21.7 (-)
20.0 (-)
4.397
PO
N
PO
13
7.6 (+)
3
2.2
36
20.9 (-)
43.6 (+)
69
50
51.1
75
3.474
N = Number of occurrences; PO = Proportion of occurrence;
the expected value
G-test
value
N
13
N
=
37.0
1.92
7.26
(+)
0.05
26.39
0.001
16.70
0.001
2.477
(+)/(-)
= food eaten above/under
(p<0.01)
%), and rodents (21.1 %). This could be a result of high availability of fruits and
and summer in temperate areas, as previously noted in studies on the food
of coyotes (Bekoff 1977) and gray foxes (Samuel and Nelson 1982).
The main foods of coyotes were rodents (Table 1), particularly cotton rats (Sigmodon
fulviventer, S. leucotis), representing 85
of rodents identified. Other rodents found in
coyote faeces included 8 occurrences of white-footed mice {Peromyscus sp.), 2 of wood rats
{Neotoma sp.) and 1 of pocket gophers (Thomomys umbrinus). Arthropods (mainly
Coleoptera and Orthoptera) were the second most frequently used food, followed by
fruits (81
of the occurrences were manzanita berries), wild ungulates (6 occurrences of
(31.2
insects in spring
%
%
white-tailed deer, Odocoileus virginianus, including 2 fawns;
1
of peccary, Dicotyles
© Biodiversity Heritage Library, http://www.biodiversitylibrary.org/
Comparative food hahits of three carnivores
in
Western Sierra Madre
1
09
I
tajacu), livestock
tails,
(mainly pigs; probably Carrion) and leporids (10 occurrences of cotton-
SylvilagHS floridanus, 3 of jackrabbits, Lepus sp.). Bird and reptiles were relatively
unimportant items.
Röderns also are the major food of coyotes in other regions (e.g, Bond 1939; Bowyer
et al. 1983). However, other investigators have reported leporids, deer, Carrion, poultry,
or fruit to be most important (Murie 1951; Bekoff 1982). Although consumed by coyotes
(YouNG 1951), insects are rarely a major part of the diet. Mammals were of lesser
importance
La Michilia coyotes than
in the diet of
for coyotes in other areas
(Bekoff
1977).
The major food item of gray foxes on our study area was fruit, manzanita berries
% of the fruit occurrences. Other important items were arthropods (mainly
comprising 96
Coleoptera), rodents (8 occurrences of white-footed mice, 6 of cotton
1
rats, 2
of
wood
rats,
of chipmunks, Eutamias hulleri) and reptiles (7 lizards and 6 snakes). Birds, Carrion (deer
remains) and cottontails were found in lesser amounts (Table
1).
La Michilia is relatively similar to other studies (Samuel and
Nelson 1982), with the exception of the low incidence of cottontails in our sample and the
relatively high number of occurrences of reptiles. Usually mammals, arthropods and fruit
The
diet of the gray fox in
constitute the bulk of the gray fox diet.
La Michilia mainly fed on arthropods (Table 1). From 244 individuals
87 % were large beetles, 3.7 % grasshoppers and 3.3 % wasps.
Pseudoscorpions and Spiders were also found. Fruits ranked 2nd and were predominated
by manzanita berries. Unidentified rodents were found in 10 % of the faeces, reptiles,
birds, Carrion (deer) and cottontails seem to be unimportant foods. Some categories that
occurred in trace amounts in the faeces, i.e., beetle larvae, fleshy fruit and other food items
The
coati in
identified
to order,
consisting of soft tissue,
may
have been underestimated in our analysis.
with those of other studies. Insects and other invertebrates of the
litter layer and a wide variety of fruit usually make up the bulk of coati foods, both in the
tropics (Kaufmann 1962) and in the drier and colder regions of the southwestern United
These
States
results agree
(Kaufmann
et al. 1976).
The feeding behaviour
of coyotes,
gray foxes, and coatis has been described as
(Chapman and Feldhammer
198.2), with availabiHty playing a major role in
comparison of diets of 3 predators allows for the analysis of
species-specific differences in prey type preference, prey size, and trophic-niche breadth.
Coyotes ate mammals more frequently, gray foxes consumed more fruits and reptiles, and
coatis relied more upon arthropods and fruit (Table 1). The diet of gray foxes appears
intermediate between those of coyotes and coatis. The trophic diversity and the size of the
major prey were largest in the coyote, intermediate in the gray fox, and smallest in the
coati. Thus, the largest predator took a greater size variety, as found by Rosenzweig
(1966), but the gray fox (whose average weight in North America is about 3.5 kg; Samuel
and Nelson 1982) took larger prey than the coati (average weight 4 to 6 kg; Kaufmann
1982). Dietary overlap was similar for the pairs coyote-gray fox (B = 0.832) and gray foxcoati (B = 0.837) and less between the pair coyote-coati (B = 0.695).
opportunistic
prey selection. However,
a
Because abundance of potential prey must be similar for the
the detected differences in prey use
may
3
predator species, some of
reflect differences in feeding ecology.
usage of Carrion, deer and probably rabbits by coyotes than by the other species
Greater
may
be
and wider ränge of movements. In the study area, cotton rats
were common in the open habitats used by coyotes in the night (Servin, pers. comm.).
The 2 other predator species are typically found in wooded habitats (Samuel and Nelson
1982; Kaufmann 1982) and rodents composed a smaller proportion of their diets. The
higher importance of rodents and the larger prey size in the diet of the gray fox in relation
to the coati possibly reflect different foraging strategies: the gray fox would have a greater
hunting abihty, while the coati collects foods from the htter layer (Kaufmann 1962).
related to their larger size
© Biodiversity Heritage Library, http://www.biodiversitylibrary.org/
M.
110
Delibes, Lucina
Hernandez and
F.
Hiraldo
Acknowledgements
gratefully acknowledge the assistance in the field of Don Federico and R. R. Estrella. The
study was supported by an agreement between the Spanish CSIC and the Mexican CONACYT,
coordinated by J. Castroviejo, Spain, and G. Halffter, Mexico, A. P. Clevenger, E. Ezcurra,
MacCracken and P. J. Polechla reviewed the manuscript. J. Servin gave us unpubhshed
J. G.
We
data.
U. Breitenmoser translated the German summary. E. Collado and N. Bustamante
also
helped.
Zusammenfassung
Vergleich der Ernährungsweise
Im Sommer
von
drei Carnivoren in der Westlichen Sierra
Madre, Mexiko
und Frühhng 1982 wurden Nahrungswahl und -Verteilung von Kojote (Canis
latrans), Graufuchs (Urocyon cinereoargenteus) und Weißrüssel-Nasenbär (Nasua narica) in der
westlichen Sierra Madre (Mexiko) untersucht. Die drei Arten waren zwar Generalisten, aber die
Kojoten ernährten sich hauptsächUch von Nagetieren, die Graufüchse von Früchten und die Nasenbären von Arthropoden. Trophische Diversität und mittlere Beutegröße waren beim Kojoten am
größten, beim Graufuchs intermediär und beim Nasenbär am kleinsten. Da das Nahrungsangebot für
alle drei Arten gleich war, scheinen die Unterschiede Abweichungen im Nahrungserwerb und in der
1981
Ökologie widerzuspiegeln.
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Miguel Delibes, Dr. Fernando Hiraldo, Estaciön Biolögica de Donana,
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Mexico
Authors' addresses: Dr.