Journal of Mammalogy, 89(4):1012–1019, 2008
SEASONAL DIET OF THE PAMPAS FOX (LYCALOPEX
GYMNOCERCUS) IN THE CHACO DRY WOODLAND,
NORTHWESTERN ARGENTINA
OMAR VARELA,* AINHOA CORMENZANA-MÉNDEZ, LUCÍA KRAPOVICKAS,
AND
ENRIQUE H. BUCHER
Instituto de Ecologı́a, Fundación Miguel Lillo, Miguel Lillo 251, Código Postal 4000, Tucumán,
Argentina (OV)
Instituto de Ambientes de Montañas y Regiones Áridas (IAMRA), Universidad Nacional de Chilecito, 9 de Julio 22,
Codigo Postal F 5360, Chilecito, La Rioja, Argentina (OV)
Centro de Zoologı́a Aplicada, Universidad Nacional de Córdoba, Rondeau 798, P.O. Box 122,
Córdoba, Argentina (EHB)
Facultad de Ciencias Naturales, Universidad Nacional de Tucumán, Miguel Llillo, Codigo Postal 4000, Tucumán,
Argentina (AC-M, LK)
The seasonal diet of Pampas foxes (Lycalopex gymnocercus) was examined from 431 scat samples collected
during 1 year in the dry Chaco woodland of Salta Province, northwestern Argentina. Fleshy fruits dominated the
diet during the dry and wet seasons, representing 69% of the total frequency and comprising 91% of the total
volume. Most of the fruit diet was contributed by 5 woody plant species. Mistol (Ziziphus mistol, Rhamnaceae),
was the most important fruit resource throughout the year. Arthropods (particularly beetles and scorpions) and
small mammals (mainly rodents and marmosets) were the most frequently consumed animal prey. Seasonal shifts
in the frequency of the main food items in the diet were not significant, but there was considerable seasonal
variation in the frequency of fruit species. Diversity of prey in the diet was highest in the wet season. The Pampas
fox is a generalist feeder that can alter its diet to changes in food availability. However, its diet in the Chaco,
which is dominated by fruit, differs from its diet in Pampas grassland habitat, where it consumes mostly meat.
Key words:
Argentina, diet, dry Chaco, frugivory, Lycalopex gymnocercus, Pampas fox
Based on the breadth and variability of their diets, carnivorous
mammals are often characterized within a spectrum ranging
from specialists to generalists (Je˛drzejewska and Je˛drzejewski
1998; Je˛drzejewski et al. 1989). Generalist species distributed
across different habitats and ecoregions may reveal large
variation in their diets, whereas specialists tend to show a rather
similar trophic niche despite significant variation in habitat
characteristics (Elmhagen et al. 2000; Kaneko et al. 2006). A
comparative analysis of resource use along geographic gradients
by a given species is therefore a useful tool for understanding its
degree of trophic specialization, information that in turn may be
useful in designing conservation strategies or improving the
efficacy of management efforts (Benson and Chamberlain 2006;
Cole et al. 1995; Connell 1975; Tokeshi 1999).
* Correspondent: [email protected]
Ó 2008 American Society of Mammalogists
www.mammalogy.org
1012
Canids (wolves, coyotes, and foxes) are a conspicuous
component of mammalian communities in South America, and
are usually the dominant group in the carnivore guild (Medel
and Jaksic 1988). They inhabit several kinds of habitat and
show high flexibility in their ecological requirements (Johnson
et al. 1996). Usually, foxes are considered generalist omnivores
that feed opportunistically on a wide variety of foods (SilleroZubiri et al. 2004). The Pampas fox (Lycalopex gymnocercus;
formerly Pseudalopex gymnocercus) is one of the commonest
carnivores in South America (Medel and Jaksic 1988). A small
(4- to 6-kg), solitary, and mainly nocturnal species, it is
relatively abundant in grasslands and open woodlands
throughout Bolivia, Paraguay, Brazil, Uruguay, and Argentina,
particularly in the Chaco, Monte, and Pampas ecoregions
(Redford and Eisenberg 1992). The distribution of the Pampas
fox in Argentina ranges from the province of Formosa in the
north to the province of Rio Negro in the south (Redford and
Eisenberg 1992).
Most of available information about food habits of the
Pampas fox refers to populations from the grassland regions of
northern Patagonia (Castillo 2002; Crespo 1971; Farı́as and
August 2008
VARELA ET AL.—DIET OF THE PAMPAS FOX
Kittlein 2008; Garcı́a and Kittlein 2005). Food habits of this
canid in scrublands and sand dune habitats (Garcı́a and Kittlein
2005) and forests (Vieira and Port 2007) have been less
studied. These studies concur in defining the Pampas fox as an
omnivore generalist, with a diet dominated by animal prey,
particularly wild mammals and insects.
In the Chaco woodland, the 2nd largest biome of South
America, the Pampas fox is probably the most common native
carnivore. The species is very abundant in areas close to human
dwellings, to the point of being considered a threat to domestic
animals. Food availability in the Chaco is likely to differ from
that in the Pampas grasslands because the preferred mammal
prey species in the Pampas, such as the European hare, do not
occur in the Chaco, and small rodents are usually less abundant,
particularly in overgrazed areas (Bucher 1982). The combination of reduced availability of mammals and abundance of fruit
and seeds in scats provided the stimuli for the present study.
Here we report the seasonal diet of the Pampas fox throughout
a 1-year study in the Chaco of Salta Province, northwestern
Argentina, based on analysis of 431 scats. Our objectives were
to describe and quantify the seasonal composition of the diet of
Pampas foxes, and to compare our results with those reported
for other biomes in Argentina and Brazil.
MATERIALS AND METHODS
Study area.— Fieldwork was conducted at Los Colorados
Biological Station and in the neighboring Campo Grande
Ranch, both sites located in Salta Province, Argentina
(248439S, 638179W). The area is a vast plain at about 200 m
above sea level. The climate is subtropical semiarid, markedly
seasonal, with a distinct warm and wet season in midspring–
summer (October–March) and a dry, cool season in autumn–
winter (April–September). Annual precipitation averages 550
mm, with 80% concentrated between December and February
(Bianchi and Yañez 1992). Mean annual temperature is 21.78C
and mean maximum and minimum temperatures are 35.88C
(December) and 7.98C (July), respectively (data from the
locality of J. V. González 1944–1950—Galmarini and Raffo
del Campo 1964). Vegetation is the typical semiarid woodland
of the Western Chaco (Cabrera 1994). Dominant trees are
Schinopsis lorentzii (Anacardiaceae) and Aspidosperma
quebracho-blanco (Apocynaceae). The most abundant
middle-sized trees are Ziziphus mistol (Rhamnaceae), Prosopis
elata (Fabaceae), and Prosopis nigra (Fabaceae). The dense
3- to 4-m-high shrub layer is dominated by species of Acacia
(Fabaceae), Capparis (Capparaceae), and Celtis (Ulmaceae),
intermingled with grasses (Varela 2001). The area around the
biological station (10,000 ha) is fenced and has been protected
from grazing by domestic herbivores for the last 30 years. In
contrast, the neighboring Campo Grande Ranch has been
subjected to continued and severe overgrazing for a longer
period, mostly by cattle and goats.
Food habits.— We used scat analysis to examine the diet of
the Pampas fox. This is a noninvasive and relatively reliable
method, and commonly used in studies of carnivore diets
(Corbett 1989; Putman 1984; Reynolds and Aebischer 1991).
1013
Fresh scats were collected from different sites frequently
visited by Pampa foxes, including paths, dirt roads, and bald
spots (‘‘peladares’’), during 5 days in each month (from
February 1995 to January 1996). All scat fragments within
0.5 m2 were considered as a single defecation. We took special
care not to collect more than 1 scat from the same place, which
could have been from the same individual. Given the spatial
and temporal distance between sampling sites, we considered
each scat as an individual foraging event. Scats were identified
by size or diameter, shape, texture, characteristic odor, deposition place, presence of hairs ingested while grooming, and
tracks close to the fecal samples. Those scats that could not be
accurately attributed to foxes were discarded.
Fecal samples were individually stored in numbered paper
bags and labeled with date of collection and location. Scats were
air dried until constant weight and then analyzed in the laboratory
following a standardized procedure (Korschgen 1987). Individual scats were weighed, manually crumbled, and then
strained through a 0.5-mm-mesh sieve to discard the inconspicuous and unidentifiable fraction, which was excluded from the
analysis. Sieve contents were placed in a petri dish and examined
under a 4–40 magnification binocular microscope. All distinguishable macroscopic components (head capsules, mandibles, legs, hairs, bones, teeth, jaws, claws, scales, vertebrae,
feathers, bones, feet, seeds, and any other identifiable remains)
were removed and identified to the finest taxonomic resolution
possible. Mammals, reptiles, and arthropods were identified by
comparison with collections of reference material deposited at
the Fundación Miguel Lillo (Tucumán, Argentina). Fruits and
seeds were identified by comparison with a reference collection
from the study area. Birds were identified only to class.
Data analysis.— We determined the importance of the each
food item in the diet in terms of 4 parameters: frequency of
occurrence, percent frequency, relative frequency, and relative
volume. We defined frequency of occurrence as the total
number of scats in which a given food item was found. Percent
frequency is the percentage of the total scats in which each
food item was found. Relative frequency is the percentage of
the total frequency in which each food item occurred. Relative
volume is the percentage of the total volume in which each
food item occurred (Korschgen 1987). The volume of each scat
sample was measured using a graduated cylinder to the nearest
1 ml. We were unable to quantify the volume for most of the
animal remains present in the scats because not all animal
species could be identified to species. To minimize overestimation of food items that contained a high proportion of
nondigestible material (e.g., arthropods with chitinous exoskeleton, fruit cuticles and fibers, nuts, and hard seeds) when
reported by frequency of occurrence (Dickman and Huang
1988; Korschgen 1987) items ,1 ml of volume were excluded
from the analysis.
We used chi-square tests (Zar 1996) to compare the total
frequency of occurrence of the main food items (fleshy fruits,
arthropods, and vertebrates) as well as to test for seasonal
differences in the frequency of occurrence of the main food
items and among the frequency of fruit species and seasons.
Seasons, defined according to rainfall pattern (dry and wet
1014
Vol. 89, No. 4
JOURNAL OF MAMMALOGY
seasons), determined pulses of fruit scarcity and abundance
(Varela 2004). Differences were considered significant at the
probability level of P , 0.01.
Trophic niche breadth and trophic diversity between seasons
were calculated using the standardized Levin index (Bstd—
Krebs 1989) and the Shannon–Wiener index (Krebs 1989),
respectively, based on frequency of occurrence of a single food
item. By food item, we considered any taxon that could be
identified in the scats. For some categories, this taxon was the
species, but higher taxonomic levels (genus or order) were used
for others. The Levins index formula is:
!1
n
X
2
B¼
pi
;
i¼1
where n is the number of food categories and p is the
proportion of records in each food item (i). The standardized
form of the formula is: Bstd ¼ (B 1)/(Bmax 1), where Bmax
is total number of food categories recognized. The scores of
this index range between 0 (minimum niche breadth) and 1
(maximum niche breadth). The Shannon–Wiener diversity
index (H) was calculated as H9 ¼ pi log2 pi, where pi is
the proportion of the frequency recorded for the item ‘‘i,’’ and
log2 is the logarithm in base 2. The diversity values obtained
were subsequently compared by Hutcheson’s test (Krebs
1989). Rarefied species accumulation curves (sensu Gotelli
and Colwell 2001) were produced by using Estimate S 8.0
(Colwell 2006) to determine whether an asymptote had been
reached, and therefore whether the diet of Pampas foxes in the
study area was adequately sampled.
RESULTS
Sampling effort.— We collected and analyzed a total of 431
scats of Pampas foxes over a 1-year period, 209 during the dry
season (April–September) and 222 during the wet season
(October–March). Based on the cumulative curves of food
items (rarefied curves) for the wet and dry seasons, which
reached an asymptotic at a sample size of about 200 scats, we
inferred that the sample size was sufficient to characterize the
seasonal diet of Pampas foxes in this study.
Diet composition.— We identified 36 different food items
(12 plants and 24 animals) .1 ml in volume (Table 1). This
number is an underestimate because we were unable to identify
all samples to species. The diet was predominantly composed
of fleshy fruits (including seeds), followed by arthropods and
vertebrates (Fig. 1). Fleshy fruits occurred in 96% of the scats,
making up 91% of the total scat volume (Fig. 1), and were
significantly more frequent than animal food categories (v2 ¼
339.3, d.f. ¼ 2, P , 0.0001).
The fruit diet comprised 13 species of fleshy-fruited plants.
Shrubs and trees were the best-represented life forms among
the 4 life forms present (Table 1). Z. mistol was the
predominant fruit in the diet, making up 48% of the total
frequency of occurrence and 58% of the total fruit volume.
Most of the fruit diet was contributed by Z. mistol, Prosopis
torquata, P. nigra, P. elata, and Acacia aroma, which together
accounted for 87% of the total frequency and for 94% of the
fruit volume (Fig. 2). Other fruits (corn and dry fruits of 3 wild
grass species) that were infrequent in the scats (volume , 1 ml)
were not considered in the analysis.
The most important animal remains were arthropods (26%),
followed by mammals (9.3%), birds (4.6%), and reptiles
(3.2%). Most of the arthropod remains were coleopterans
(21.3%; particularly Tenebrionidae and Scarabidae) and
scorpions (7.4%). The most frequently found mammals were
small rodents (6.3%) and mouse opossums (1.2%). Mediumsized mammals such as Dolichotis salinicola (Rodentia) and
Sylvilagus brasiliensis (Lagomorpha) appeared in only 1 scat
sample. Remains of domestic mammals (goats and cows) were
occasionally present in the scats (0.7%) and contributed
a negligible volume (0.3%). Birds and reptiles (lizards and
nonvenomous snakes) accounted for small part of the overall
volume (1.1% and 0.9%, respectively). Neither amphibians nor
fishes were present.
Seasonal use of food.— There were no significant differences
in the number of occurrences of the main food categories
(fleshy fruits, arthropods, and vertebrates) between seasons
(chi-square test of association: v2 ¼ 3.13, d.f. ¼ 2, P ¼ 0.21;
Fig. 1). However, the frequency of occurrence of fruit species
(Fig. 2) was significantly different between seasons (chi-square
test of association: v2 ¼ 90.74, d.f. ¼ 11, P , 0.0001). The
partial components of chi-square showed that the differences
occurred mainly due to the unequal frequency of fruits of A.
aroma and Prosopis between seasons. Fruits of A. aroma were
more frequent than expected in the dry season during its peak
of availability, whereas the opposite happened with the
frequency of occurrence of fruits of Prosopis (P. nigra and
P. elata). Fruits of Z. mistol were highly consumed in each
season (Fig. 2).
Trophic niche breadth.— Dietary breadth of Pampas foxes
was slightly higher in the wet season (Bstd ¼ 0.205) than in the
dry season (Bstd ¼ 0.195). Likewise, the trophic diversity of the
diet was significantly higher in the wet season (H9wet ¼ 3.82) as
compared to the dry season (H9dry ¼ 3.44; t ¼ 3.22, d.f. ¼ 895,
P , 0.01).
DISCUSSION
Our study confirms the generalist–omnivorous nature of the
diet of the Pampas fox, as compared with previous studies
(Crespo 1971; Farı́as and Kittlein 2008; Garcı́a and Kittlein
2005; Vieira and Port 2007). Prey types ingested by Pampas
foxes in our study area are similar to what was found in other
regions of the fox’s distribution, although several species
identified here have not been previously reported as part of the
diet of Pampas foxes (Table 1). We cannot determine whether
the observed differences resulted from differences in seed
availability between sites or, alternatively, the new diet items
did not occur in grassland sites where the diet of Pampas foxes
has been reported.
The most striking difference between our results and those of
previous studies is the considerably higher proportion of fleshy
fruits taken by foxes from the Chaco, which contrasts with the
prevalence of animal matter in the diet of Pampas foxes from
other regions. Fleshy fruits comprised more than two-thirds of
August 2008
VARELA ET AL.—DIET OF THE PAMPAS FOX
1015
TABLE 1.—Diet composition of the Pampas fox (Lycalopex gymnocercus; scat analysis) in the Chaco dry woodland of Salta, northwestern
Argentina, sampled during the wet and dry seasons of 1995. Values indicate number of each item that occurred in scats (FO), percentage of the
total scats in which each food item was found (FO (%)), and percentage of the total volume in which each food item occurred (RV (%)).
Unidentified items (NI) are specified in parentheses. n ¼ number of scats. The life forms are defined according to Zuloaga and Morrone (1996).
A plus (þ) indicates species included in the Pampas fox diet that are listed for the 1st time.
Wet season (n ¼ 222)
Food items
Species (family) (life form)
Fleshy fruits
þAcacia aroma (Fabaceae) (shrub)
þAcanthosyris falcata (Santalaceae) (tree)
þBromelia hieronymi (Bromeliaceae) (herb)
þCapparis speciosa (Capparaceae) (shrub)
þCeltis pallida (Ulmaceae) (shrub)
Geoffroea decorticans (Fabaceae) (tree)
þGrabowskia duplicata (Solanaceae) (shrub)
þProsopanche americana (Hydnoraceae) (parasite)
þProsopis (P. nigra þ P. elata) (Fabaceae) (tree)
þProsopis torquata (Fabaceae) (shrub)
þXimenia americana (Olacaceae) (shrub)
þZiziphus mistol ( Rhamnaceae) (tree)
Arthropods
Coleoptera
Anoploderma (Cerambycidae)
Aplagiognathus (Cerambycidae)
þCalocomus desmaresti (Cerambycidae)
Dichotomius (Scarabaeidae)
þEntomoderes satanicus (Tenebrionidae)
Glyphoderus (Scarabaeidae)
Megelenophorus (Tenebrionidae)
Pelidnota (Scarabaeidae)
Pinotus (Scarabaeidae)
þPsectrascelis ursina (Tenebrionidae)
Strategus (Scarabaeidae)
þScotobius hystricosus (Tenebrionidae)
Orthoptera (NI)
Scolopendromorpha
þScolopendra viridicornis (Scolopendridae)
Scorpiones
Timogenes (Bothriuridae)
þTimogenes dorbignyi (Bothriuridae)
Vertebrates
Mammals
Wild mammals
Didelphimorphia
Thylamys pusillus (Didelphidae)
Lagomorpha
þSylvilagus brasiliensis (Leporidae)
Rodentia
þDolichotis salinicola (Caviidae)
Galea musteloides (Caviidae)
Microcavia australis (Caviidae)
þGraomys griseoflavus (Muridae)
Domestic mammals
Artiodactyla
Bos taurus (Bovidae)
Capra hircus (Bovidae)
Birds (NI)
Reptiles
Sauria (lizards) (NI)
Serpentes (snakes) (NI)
Dry season (n ¼ 209)
FO
FO (%)
RV (%)
FO
FO (%)
RV (%)
214
15
11
6
12
12
1
1
8
59
48
5
140
96.4
6.8
5.0
2.7
5.4
5.4
0.5
0.5
3.6
26.6
21.6
2.3
63.1
89.2
3.8
4.7
0.9
1.2
1.0
0.3
,0.1
0.4
23.3
5.0
0.4
48.2
195
58
0
12
1
0
0
1
10
16
42
0
151
93.3
27.8
0.0
5.7
0.5
0.0
0.0
0.5
4.8
7.7
20.1
0.0
72.2
92.5
22.8
0.0
0.8
0.1
0.0
0.0
0.07
0.9
4.4
5.7
0.0
57.6
67
30.2
6.1
45
21.5
3.4
58
1
6
1
29
10
1
0
1
1
31
29
16
2
1
1
13
10
1
26.1
0.5
2.7
0.5
13.1
4.5
0.5
0.0
0.5
0.5
14.0
13.1
7.2
0.9
0.5
0.5
5.9
4.5
0.5
4.7
—
—
—
—
—
—
—
—
—
—
—
—
0.1
,0.1
—
1.4
—
—
34
0
0
0
7
10
1
1
0
0
28
22
11
0
1
1
19
11
7
16.3
0.0
0.0
0.0
3.3
4.8
0.5
0.5
0.0
0.0
13.4
10.5
5.3
0.0
0.5
0.5
9.1
5.3
3.3
2.4
—
—
—
—
—
—
—
—
—
—
—
—
0.0
0.16
—
0.9
—
—
35
16
15.8
7.2
4.7
1.8
39
27
18.7
12.9
4.1
3.0
14
0
0
0
0
11
1
1
3
4
2
2
1
1
6.3
0.0
0.0
0.0
0.0
5.0
0.5
0.5
1.4
1.8
0.9
0.9
0.5
0.5
1.3
—
—
—
—
—
—
—
—
—
0.5
—
0.3
0.2
26
5
5
1
1
17
0
4
4
9
1
1
1
0
12.4
2.4
2.4
0.5
0.5
8.1
0.0
1.9
1.9
4.3
0.5
0.5
0.5
0.0
2.9
—
—
—
—
—
—
—
—
—
0.1
13
5.9
1.3
7
3.3
0.9
8
5
5
3.6
2.3
2.3
1.5
—
—
6
2
5
2.9
1.0
2.4
0.2
—
—
0.1
0.0
1016
JOURNAL OF MAMMALOGY
Vol. 89, No. 4
FIG. 1.—Seasonal composition of major food items in the diet of
Pampas foxes (Lycalopex gymnocercus) in the Chaco dry woodland of
Salta, Argentina. Bars indicate the percentage of the total frequency or
total volume in which each food item occurs. Number in parentheses
indicates sample size.
the diet of Pampas foxes in the Chaco dry woodland of Salta, as
compared with only one-fourth of the diet in the grasslands of
La Pampa Province (Crespo 1971). Moreover, recent studies
(Castillo 2002; Farı́as and Kittlein 2008; Garcı́a and Kittlein
2005; Vieira and Port 2007) conducted in different habitats
(grasslands, scrublands, sand dunes, and forests) also agree in
that Pampas foxes feed mainly on animal prey (particularly
mammals and insects). In such studies, fruits were important in
certain seasons only, whereas in the Chaco dry woodland fruits
dominated the diet of Pampas foxes throughout the year. The
ability of Pampas foxes to survive on a low-meat diet in the
Chaco is comparable to the differences in diet of Darwin’s fox
(Lycalopex fulvipes) between the Island of Chiloe and
continental areas of Chile (Jimenez et al. 1991).
The regional differences observed in the diet of Pampas
foxes possibly are a response to food availability. Although our
study does not provide data on this aspect, it is well known that
availability of fleshy fruits is relatively higher in the Chaco
woodland than in the grassland habitats, where most of the
FIG. 2.—Seasonal composition of fruit species in the diet of Pampas
foxes (Lycalopex gymnocercus) in the Chaco dry woodland of Salta,
Argentina. Bars indicate the percentage of the total frequency or total
volume in which each food item occurs. Number in parentheses
indicates sample size.
fruit-producing trees and shrubs are rare or absent. Moreover,
rodents are relatively scarce in the Chaco (Chani et al. 1998).
European hares (Lepus europaeus), the most commonly
consumed prey in the Pampas (Crespo 1971), also are absent
in our study area.
The use of fleshy fruits by Pampas foxes closely agrees with
fruiting patterns in the study area. Fleshy fruits were slightly
more diverse in the diet during the wet season, when more
plant species have ripe fruits. The high rate of fruit
consumption by Pampas foxes in the Chaco dry woodland is
comparable to few examples recorded in the canid literature
(Geffen et al. 1992; González del Solar et al. 1997; Hockman
and Chapman 1983; Jimenez et al. 1991) and confirms recent
studies showing the species’ importance as a fruit-dispersal
agent (Varela 2004; Varela and Bucher 2006).
August 2008
VARELA ET AL.—DIET OF THE PAMPAS FOX
It has been well documented that the diet of canids responds
to shifts in seasonal availability of food (Castillo 2002;
Elmhagen et al. 2000; Hockman and Chapman 1983; Kaneko
et al. 2006; Motta-Junior et al. 1996; Pigozzi 1992). According
to the energy optimization model (MacArthur and Pianka
1966), generalist species increase their feeding efficiency by
shifting to other food resources when fleshy fruits become
scarce. Our results show that the proportion of fruit in the diet
of Pampas foxes remained relatively constant throughout the
seasons, despite changes in the proportions of fruit species.
Of particular interest is the high proportion of fruit consumed
by Pampas foxes during the period of highest fruit scarcity (dry
season: July–October), when only a few woody plants species
(e.g., Z. mistol, A. aroma, and Caesalpinia paraguariensis) are
fruiting in the study area. Preference for fruits of Z. mistol may
be explained by several reasons: the long fruiting season of this
species (from mid-October to late July); regular productivity
(we observed plants fruiting every year during 10 consecutive
years); prolonged availability of undamaged fruits on the
ground, which is favored by the low water content of the fruits
as well as low humidity and relatively low temperatures during
the dry season; high palatability observed in captive individuals; and high availability (mistol is the 2nd most abundant
woody species with fleshy fruits in the study area—Varela
2004). The fruit of Z. mistol also may be preferred because of
its nutritional content, although data on this aspect are not
available. Chemical studies of fruits of congeneric species,
such as Z. jujuba (Guil-Guerrero et al. 2004), Z. mauritiana
(Muchuweti et al. 2005), and Z. obtusifolia (Everitt 1986),
showed the presence of fatty acids, proteins, and sugars.
Although a wide variety of fruit species were available, the
Pampas fox appears to be highly selective. Fruits of some very
abundant species (e.g., Castela coccinea and Capparis
tweediana) were not included in the diet of Pampas foxes.
Chemical compounds (triterpenoids, alkaloids, and phenols)
present in these fruits may act as feeding deterrents for the
three-banded armadillo (Tolypeutes matacus—Bolkovı́c et al.
1995) and probably also for the Pampas fox. The fruits of C.
tweediana might have similar compounds, because it has been
reported that Chaco aborigines washed the seeds to eliminate
the chemical compounds present in the fruit pulp (Arenas
1981).
Meat from domestic animals (young goats and cows) was
occasionally present in the scats. It is likely that Pampas foxes
occasionally scavenge on carrion (Crespo 1971), because it is
unlikely that Pampas foxes would be able to kill a goat or
sheep. We conclude therefore that in our study area predation
by foxes on domestic livestock is insignificant.
Our findings support previous studies indicating that the
Pampas fox is an omnivorous and generalist feeder that can
adapt its diet to changes in food availability (Castillo 2002;
Crespo 1971; Vieira and Port 2007). However, examination of
our data also shows the high dominance of fruit (especially of
Z. mistol) as a staple in the diet of Pampas foxes in the Chaco,
suggesting that in the Chaco, Pampas foxes have a more
1017
significant role as fruit eaters and seed dispersers than as
vertebrate predators.
RESUMEN
Se analizó la dieta estacional del zorro Pampa (Lycalopex
gymnocercus) en los bosques del Chaco seco de la provincia de
Salta, noroeste de Argentina, a partir de 431 heces colectadas
durante 1 año. Los frutos carnosos dominaron la dieta tanto en
estación húmeda como la seca, contribuyendo el 69% de la
frecuencia total y el 91% del volumen total. La mayor parte de
la dieta de frutos fue aportada por cinco especies de plantas
leñosas. El mistol (Ziziphus mistol, Rhamnaceae) fue la fuente
de alimento más importante durante el año. Los artrópodos
(principalmente escarabajos y escorpiones) y los micromamı́feros (especialmente roedores y marmosas) fueron las presas
consumidas con mayor frecuencia. No hubo cambios estacionales significativos en la frecuencia de los principales ı́tems de
alimentos en la dieta, pero hubo marcada estacionalidad en la
frecuencia de las especies con frutos carnosos. La diversidad de
presas en la dieta fue más alta durante la estación húmeda. Los
resultados confirman que el zorro Pampa es un omnı́voro
generalista que puede adaptar su dieta a la disponibilidad de
alimentos. Sin embargo, su dieta en el Chaco está dominada
por frutos, mientras que en el hábitat de pradera de la consiste
principalmente de carne.
ACKNOWLEDGMENTS
We thank the Fundación para Desarrollo del Chaco for giving
permission and logistical support to conduct this research at Los
Colorados Biological Station. Fieldwork was financially supported by
the World Wildlife Fund (grant FA91) and Consejo Nacional de
Investigaciones Cientı́ficas y Técnicas of Argentina, granted to EHB,
and a research fellowship provided by Consejo Nacional de
Investigaciones Cientı́ficas y Técnicas of Argentina to OV. Several
researchers (G. Claps, P. Ortiz, P. Jayat, J. C. Moretta, and M. Tome)
provided substantial assistance in the identification of animal specimens. M. Beleizán provided invaluable assistance in fieldwork.
J. Brasca checked the English language. We are especially grateful to
F. Beleizán and L. Gil from Campo Grande for their friendship and
hospitality, which made our stay in the study area comfortable and
pleasant.
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Submitted 28 April 2007. Accepted 18 January 2008.
Associate Editor was Rodrigo A. Medellı́n.