Fox Stomachs Research Articles

Occurrence of ingested human litter in winter arctic foxes (Vulpes lagopus) from Svalbard, Norway

The aim of this study is to assess the occurrence of human litter ingested by arctic foxes (Vulpes lagopus) caught in Svalbard, Norway, in winter when scavenging is at its highest. Twenty arctic fox stomachs and intestines were examined for human litter and plastic using the protocol from the Oslo-Paris Convention (OSPAR) for monitoring plastic ingestion by the northern fulmar (Fulmarus glacialis) (human litter and plastic >1 mm). The arctic foxes had ingested human litter at a low frequency (15%, 3 out of 20 foxes). Despite the low sample size, we do not regard ingestion of human litter as an immediate threat to the arctic fox population in Svalbard.

The Diet of Foxes and the Availability of Anthropogenic Food on Prince Edward Island, Canada

It has been postulated that red foxes (Vulpesvulpes) inhabiting Prince Edward Island National Park (Canada) make very little use of natural food sources and that anthropogenic food play an integral part in their diet. The use of anthropogenic food sources has also been associated with an increased number of fatal fox vehicle-collisions in the park. The main goal of this study was to examine the composition of the diet of foxes inhabiting Prince Edward Island National Park and to compare this diet with foxes found in other areas of the island. In particular, we examined the importance of anthropogenic food items in foxes inhabiting the national park. We analyzed 38 stomachs from foxes killed by trappers or vehiclesduring late fall and early winter within and outside the national park. Our results showed that rodents and vegetation were the most common food items present in fox stomachs whether the animals were obtained from within or outside the park. Values of coefficient of variation of food items found in fox stomachs indicated a great diversity in diet composition. However, only six stomachs contained anthropogenic food items. Stomachs of foxes killed by vehicles contained twice the amount of anthropogenic food items than those that were collected from trappers. Overall, our findings indicate that anthropogenic food items are only a minor component in the diet of foxes occurring within the park, at least during the period of time examined in this study. Future studies should examine diet composition during other seasons when the quantity and quality of anthropogenic food sources is different.

Prey selectivity by feral cats at central Australian rock-wallaby colonies

Threatened warru, or black-footed rock-wallaby (Petrogale lateralis MacDonnell Ranges race), populations in northern South Australia continued to decline despite baiting for foxes (Vulpes vulpes), which improved their short-term conservation status elsewhere. To investigate whether feral cats (Felis catus) also represent a risk to warru we compared frequencies of prey occurrence in 103 feral cat and 14 fox stomachs shot near warru colonies in northern South Australia during 2001–17 with measures of prey abundance from pitfall trapping and opportunistic searches. We hypothesise that one fresh adult warru kill and the presence of warru remains in four other cats suggests predation by cats on adult and juvenile warru. Small reptiles and invertebrates were the most frequently recorded prey of cats in summer, whereas rodents and small dasyurids were the most frequent prey items in winter. Small mammals, small snakes and pygopodid lizards were over-represented in the diet of cats compared with estimated encounter frequencies, whereas fast-running dragons, knob-tailed geckoes (Nephrurus) and echidnas (Tachyglossus aculeatus) were not recorded from cat stomachs despite being relatively abundant. Rabbits (Oryctolagus cuniculus), rodents and fruits were the most frequently recorded items in fox stomachs. This study reinforces that targeted management of feral cat populations should be considered in concert with control of canids in sustainable recovery programs for warru and other cat-vulnerable species.

Variation in the feeding pattern of red foxes in relation to changes in anthropogenic resource availability in a rural habitat of western Poland

The feeding pattern of red foxes Vulpes vulpes, i.e., the composition of their diet and dietary responses to fluctuations in the abundance of common voles Microtus arvalis were compared in the periods before and after the limitation of anthropogenic food availability in a rural area in western Poland. During the winter seasons of 1996/97–2014/15, the diet of the foxes was estimated by analysing the stomach contents of individuals shot from November to March and the index of vole abundance was obtained by counting their burrow entrances. The major component of the fox diet over the entire study period was anthropogenic food (mainly, the remains of farm animals) that showed both the highest average proportion in the stomach content volume (53.4%) and the highest average frequency of occurrence in the stomachs (62.7%), whereas small mammals were the second important component (27.5% and 54.2%, respectively). The frequency of anthropogenic food decreased and the frequencies of wild ungulate carrion and other wild vertebrates (mainly birds) increased after the limitation of anthropogenic resources. The observed fluctuations in the index of vole abundance resulted in positive changes in the small mammal frequency and negative changes in the anthropogenic food frequency, but the course of these relationships did not significantly differ between the two periods. The frequency of hares in fox stomachs did not change significantly between these periods, but recently the occurrence of hares in the diet of foxes increased with vole abundance. This study indicated that the reduction of anthropogenic food availability for carnivorous mammals may result in their switching to other prey species and potentially may have a negative influence on the demography of such prey species.

The diet of Danish red foxes (Vulpes vulpes) in relation to a changing agricultural ecosystem. A historical perspective

Rodents and especially voles (Microtus agrestis or arvalis) make up the basic diet of foxes (Vulpes vulpes) in Denmark. As the abundance of voles and mice may have decreased as a result of modern agricultural procedures, this study investigates potential changes in the diet of Danish red foxes over the past 4 decades in relation to a changing agricultural landscape. Our study compares the stomach contents of foxes collected in Jutland during the years 2012–2014 with a similar study from 1965 to 1970. The results show that small rodents occur in the stomachs of foxes with the same frequencies today (73 %) as 40–50 years ago (67 %), while the frequency of European brown hare (Lepus europaeus) has decreased from 7 to 3 % and the frequency of roe deer (Capreolus capreolus) has increased from 3 to 18 %. The changes in the occurrence of brown hare and roe deer in the diet of foxes during the past 40 years most probably reflect changes in the populations of the two species. By comparing digitised orthophotos of six agricultural areas (3.5 × 3.5 km) of the past 1974/1975 and present landscapes, it was revealed that the total area of crop fields, small natural habitats, hedgerows and grasslands have remained almost unchanged. However, mean field size has increased by 48 %, and the mean size of small natural habitats has increased by 15 %; meaning that the length of field boundaries and the number of small natural habitats have decreased by 65 and 33 %, respectively. The distance between natural habitats in the cultivated areas has become larger during the past 40 years. Overall, the areas of natural biotopes have remained the same in Denmark during the past 40 years. Field boundaries on the other hand which are known to be important vole habitats have become fewer in the cultivated areas. Despite this, small rodents still occur in high frequencies in the diet of nowadays foxes. As voles are sensitive to fragmentation, narrow stipes of permanent grass should be maintained or even re-established in the cultivated areas to improve life conditions for small rodents and other wildlife.

Factors affecting the diet of the red fox (Vulpes vulpes) in a heterogeneousMediterranean landscape

The diet of the red fox (Vulpes vulpes) has been well studied in Europe, but limited information exists about its feeding habits in Greece and in other Mediterranean landscapes. We studied the diet variation of the red fox by analyzing contents from 219 red fox stomachs in central Greece from 2003 to 2005. We used canonical correspondence analysis (CCA) and quasi-distribution generalized linear model (GLM) response curves to investigate whether the trophic groups of the red fox diet varied temporally and/or spatially with environmental factors. Mammals, arthropods, and plants were the most important trophic groups in the diet; in particular, the European brown hare (Lepus europaeus) was consumed significantly more within hunting areas. The CCA produced a significant model for the response (trophic groups) and predictor datasets (environmental, spatial, and temporal variables). In addition, GLM response curves resulted in 13 best-fitted complexity models, which were evaluated with the Akaike information criterion. The results demonstrated 4 basic predation patterns. First, the red fox showed an opportunistic exploitation of food resources according to seasonal appearance, with temporal gradients being the main drivers affecting predation. Second, the red fox had a generalist diet, consuming cold-blooded vertebrates, arthropods, birds, and small-sized carnivores in a highly seasonal way. Third, the diet showed uniform predation on small mammals in all habitat types during the study. Finally, the red fox relies on hares within hunting areas, irrespective of habitat type or temporal gradients. Additional and long-term studies are needed to understand in depth the mechanisms involved in those observed high predation rates on hares.

Echinococcus multilocularis in Graubünden: Verbreitung bei Füchsen und Vorkommen potentieller Zwischenwirte

The southern border of the European endemic area of Echinococcus multilocularis runs along the alpine crest. This endemic transition area was analysed in the canton Grisons on a small spatial scale. A total of 543 foxes originating from 10 areas north and 4 areas south of the main alpine divide were investigated. Parasites were isolated using the sedimentation and counting technique on intestinal contents. The mean prevalence of E. multilocularis was 6.4% with significant differences between different areas. In the southern valleys, only foxes from the Val Müstair were infected (14.3%). On the northern side of the main alpine divide, prevalences varied between 0 and 40%. The predation habits of foxes on potential intermediate hosts was investigated by means of stomach content analyses (n=530). Rodents of the genera Microtus/Pitymys were found in 19.6% of fox stomachs, Clethrionomys glareolus in 8.0% and Arvicola terrestris in 0.4%. A small scale analysis based on a 10 x 10 km grid suggested that the predation rate on the genera Microtus/Pitymys significantly correlated with the prevalence of E. multilocularis in foxes (Spearman's r = 0.51). Hence, E. multilocularis appears to occur in the alpine study area on a very small spatial scale. These local sources of infection may persist for decades. This may partly explains why, during the last 34 years, some human cases of alveolar echinococcosis occurred in areas of the Canton Grisons where the parasite is presently endemic in foxes. No such human cases have been recorded in other areas free of E. multilocularis.

Effects of the seasonal availability of short-tailed shearwaters (Puffinus tenuirostris) on the diet of red foxes (Vulpes vulpes) on Phillip Island, Victoria

The diet of red foxes (Vulpes vulpes) on Phillip Island, Victoria, was assessed from the frequency of occurrence and volume of food items in stomachs of foxes killed during a 16-year control program (1983 to 1998). Of the 289 stomachs examined, 244 (85%) contained recognisable food items. Based on frequency of occurrence, the most common prey were short­tailed shearwaters (Puffinus tenuirostris, 47%), European rabbits (Oryctolagus cuniculus, 30%), house mice (Mus musculus, 15%), insects (15%), little penguins (Eudyptula minor, 12%), other birds (12%), sheep (Ovis aries 8%) and black rats (Rattus rattus 5%). The seasonal attendance patterns of P. tenuirostris caused substantial variations in the fox diet. When P. tenuirostris were present, between September and April each year, they were the most common food item, and when absent, they were replaced by rabbits. The sex of foxes did not appear to influence diet, but age did. Juvenile (Rubus fructicosus), than did adult foxes.

Vole Cycles, Snow Depth and Fox Predation

Throughout the years, Oikos has recurrently lent its pages to discussions over Fennoscandian vole cycles in general and the role of predation in particular. One conceptual model that has emerged considers delayed density dependent predation during the decline to low phase by specialist predators as one possible driving force behind the cycles in the north, and an overall high predation by generalist predators as the cause of stability or noncyclicity in the south (Hansson 1979, 1987; see also Erlinge et al. 1983, 1984, 1988, and Erlinge 1987). An intermediate zone is characterized by weakly cyclic or semi-cyclic vole populations (Hansson and Henttonen 1985, 1988, Korpimaki 1986). The delayed predation pressure in the north is suggested to be partly due to low densities and low diversity of alternative prey, which cannot buffer the variations in vole abundance. For example, rabbit (Oryctolagus cuniculus L.), brown hare (Lepus europaeus, Pall.), and wood mice (Apodemus spp.) are alternative prey species that occur only or mainly in the southern parts of Sweden (Siivonen 1976). Consequently, the population density of the red fox (Vulpes vulpes L.) exhibits cyclical fluctuations in northem Sweden. In southern Sweden, the diet of foxes is more diverse (Angelstam et al. 1984), and the population density is more stable (Lindstrom 1982, Angelstam et al. 1985). Another important component of the assumed mechanism is the lack of a reliable snow-cover during winter in the south. This should increase the vulnerability of voles to predation. The average duration of snow-cover varies between 20 and 120 d in southern Sweden and between 150 and 220 d in most of northern Sweden (Angstrom 1974). Grimso Wildlife Research Area (59'40'N, 15'25'E) is situated in the intermediate zone concerning vole fluctuations. There, we studied field vole (Microtus agrestis L.) fluctuations by snap-trapping, and red fox diet by scat and stomach analyses, during 1973-1992. According to the model, we should expect a cyclic-like pattern of fluctuations in which delayed density dependent predation by foxes and other predators plays a role. However, this pattern might be disturbed by an increased overall predation pressure during winters of little snow. Field voles did indeed exhibit a fluctuation pattern resembling regular 3-4-yr cycles, though with variable peak densities (Fig. 1). However, the interrupted increase during 1980-81 and the regular winter decreases and low densities during the last 3 yr of the series (1989-1992) all coincided with winters of little snow (measured on 15 Feb., Fig. 1). In fact, over-winter population change, calculated as spring index/previous autumn index, was significantly positively related to snow depth when adjusted for increase, decrease or no change from previous to present spring (multiple linear regression: n = 14 [5 cases omitted: autumn index = 0; 0 or 1 vole caught following spring]; R2 = 0.58; total F = 7.70, P = 0.004; snow depth F = 4.82, P = 0.025; spring-spring change F=7.47, P=0.01, Fig. 2). All P-values in this text are 1-tailed. The density of adult foxes (indexed during spring) in the Grimso area tracked field vole density, but with a time lag of one year (Lindstr6m 1989). The fluctuations in density were primarily due to variations in reproductive success. Field voles constituted 66% of all small rodents determined to species in fox scats during 1975-1979 (Lindstrom 1982). The only other species that occurred in significant amounts (27% of all small rodents) was the bank vole (Clethrionomys glareolus Shreb.). Both these species exhibited synchronous population fluctuations in the Grimsb area as well as in northern Sweden (Hornfeldt 1991, in press). Field voles were equally important in fox stomachs, whereas bank voles and mice (Apodemus spp. and Mus musculus L.) each constituted 13% of all small rodents. During 1982-1986, the predominance of field voles in the diet of foxes was still higher (ratio field

Diet of red foxes (Vulpes vulpes) in South-west New South Wales, with relevance to lamb predation.

The diets of 212 foxes (Vulpes vulpes) in the far south-west of New South Wales were determined between 1985 and 1989 and compared with other Australian studies. Mammalian remains, at an overall occurrence of 99.1%, formed the basis of the diet during the autumn and winter months. The most frequently occurring mammals were rabbits (Oryctolagus cuniculus) (34.9%), sheep (Ovis aries) (30.7%) and macropods (Macropus spp.) (20.3%). Insects occurred in 31.1% of stomachs and formed a substantial proportion of the diet. Fresh newborn lamb was identified in only 3.8% of all stomachs, but evidence of lamb consumption was 10 times greater (35.2%) from foxes collected near lambing flocks. Other studies around lambing flocks have also shown a high occurrence of fresh lamb in fox stomachs and there is circumstantial evidence that predation of lambs by foxes can be common. It was concluded that lamb predation is likely to be severe where the fox population density is high, where older foxes predominate, and where alternative preferred foods are scarce. More research is required to confirm these observations.

Similarities and contrasts in the diets of foxes, Vulpes vulpes, and cats, Felis catus, relative to fluctuating prey populations and drought

The diets of the fox, Vulpes vulpes, and feral cat, Felis catus, were studied at Yathong Nature Reserve in semi-arid western New South Wales. The overall occurrence of rabbit was 45.1% in stomachs of foxes and 54.0% in cats, representing 51.3 and 82.6% respectively of the weight of stomach contents. Both predators exhibited a functional response to rabbits, Oryctolagus cuniculus, (their staple prey) during the rabbit breeding season. Predation on rabbits was greatest on an increasing prey population during good pasture conditions and a decreasing population during drought. After the rabbit breeding season, diet changed to other prey and resulted in an annual prey cycle which was similar for foxes and cats. Both predators successfully co-exist in the semi-arid environment by primarily utilising different age groups of the same staple prey and to some extent different supplementary prey. Foxes mainly ate adult rabbits and cats young rabbits. During the drought foxes preyed heavily on adult rabbits; cats ate some rabbits but relied heavily on other food sources. The supplementary prey of foxes were invertebrates, birds, reptiles and carrion; small mammals and fruits opportunely eaten. Invertebrates, birds, reptiles and small mammals were supplementary prey for cats with carrion opportunely eaten.

Condition and growth and Red Foxes (Vulpes vulpes) in relation to food supply

Fat deposits of463 Red fox vixens shot during autumn‐winter were monitored throughout a four‐year cycle of vole abundance (1975‐79) in south‐central Sweden. The growth ofjuveniles during the same period was indexed by lower jaw length during winter. The reproduction of foxes in the study area was correlated with vole abundance. Fat deposits built up during autumn and were depleted during winter. Subadults had consistently smaller fat deposits than adults. There was no positive correlation between vole abundance and mean fat deposits in autumn or degree of depletion during winter. The mean amount of fat deposited during autumn was correlated with the frequency ofoccurrence offruit and berries in fox stomachs. The degree of depletion of fat deposits during winter was correlated with mean snow depth. It is hypothesized that the availability of fruit and berries (a major source of carbohydrates in the diet of foxes) determines the amount of fat reserves built up during autumn, whereas the energy requirement of moving in deep snow determines the degree of depletion during winter. Juvenile growth was correlated with vole abundance but growth later in life seemed to compensate for this variation.

A Study of the Fleas of Cottontail Rabbits in New Jersey

(Ecology, 36: 366-367, 1955) found pheasant in only three. Hatfield (Journ. Mamm., 20: 204, 1939) found pheasant in four of 29 stomachs of Minnesotataken red foxes. In an extensive survey of food habits of foxes in Wisconsin and Iowa, Errington (Journ. Mamm., 16: 192-200, 1935) found no pheasants in 46 winter-taken red foxes from Wisconsin, and four in 50 red and two gray fox stomachs taken in winter in Iowa. In an examination of the