Fox Density Research Articles

Effects of long‐term fox baiting on species composition and abundance in an Australian lizard community

Abstract We report on the effects of almost a decade of 1080‐fox baiting on a lizard community in a mosaic Australian habitat. Replicated comparisons of baited versus non‐baited control areas with near‐identical histories of bush fires, grazing and climate showed a higher density of red fox tracks (Canis vulpes) in the non‐baited areas. Furthermore, the fox‐baited areas showed a more than five times higher density of sand goannas (Varanus gouldii), a species that strongly overlaps the red fox in food niche breadth and is itself a direct target of fox predation, in particular its eggs and young. Exclusion of predators from a natural habitat led to significant increases in the density of small lizards, suggesting that predation can drive lizard population dynamics in this ecosystem. Replicated pitfall‐trapping in three habitats in the control areas (with high fox and low goanna density) versus the baited areas (with low fox and high goanna density) showed that fox baiting had positive effects on the density of diurnal scincid lizards in open grassland, whereas the control areas showed higher density of nocturnal gecko lizards. Our interpretation is that fox removal may result in a shift in the top predator towards the sand goanna. Historically, this indigenous, endemic species was the natural top predator. It has co‐evolved with its prey and that may have moulded it into a more efficient lizard predator per encounter than the introduced fox.

Assessment of scat-detection dog surveys to determine kit fox distribution

Developing sound conservation strategies for carnivores in fragmented landscapes relies on accurate distribution information. Fecal (scat) surveys can provide an effective survey technique, especially when collection of scats is followed by genetic analysis of DNA extracted from scats. Furthermore, use of specially trained detection dogs to locate scats on survey routes may greatly enhance scat recovery. We evaluated utility of scat-detection dog surveys as a method to determine current distribution of kit foxes (Vulpes macrotis mutica). We used a trained dog to locate scats in core and satellite population areas with various densities and different habitat conditions. We compared number of scats found per kilometer on transects along different road and vegetation types. Scat-detection dog surveys detected the presence of kit foxes in each population area searched, regardless of relative fox density and vegetation type. We found a greater number of scats on unpaved than paved roads, suggesting unpaved roads are more appropriate for monitoring of foxes. Additionally, we found a greater number of scats in saltbush (Atriplex polycarpa) scrub than in non-native grassland. This result was strongly influenced by latitude, and was probably related to a north-south precipitation gradient. Our results demonstrate that scat-detection dog surveys can provide an effective conservation tool to map current kit fox distribution. This survey method has a wide application to other carnivore species, and can be used to survey multiple species simultaneously.

Echinococcosis, Ningxia, China

Echinococcosis, Ningxia, China

Predictors of Red Fox (<em>Vulpes vulpes</em>) Helminth Parasite Diversity in the Provinces of Spain

We analysed the viscera of 321 red foxes collected over the last 30 years in 34 of the 47 provinces of peninsular Spain, and identified their helminth parasites. We measured parasite diversity in each sampled province using four diversity indices: Species richness, Margalef's species richness index, Shannon's species diversity index, and inverse Simpson's index. In order to find geographical, environmental, and/or human-related predictors of fox parasite diversity, we recorded 45 variables related to topography, climate, lithology, habitat heterogeneity, land use, spatial situation, human activity, sampling effort, and fox presence probability (obtained after environmental modelling of fox distribution). We then performed a stepwise linear regression of each diversity index on these variables, to find a minimal subset of statistically significant variables that account for the variation in each diversity index. We found that most parasite diversity indices increase with the mean distance to urban centres, or in other words, foxes in more rural provinces have a more diverse helminth fauna. Sampling effort and fox presence probability (probably related to fox density) also appeared as conditioning variables for some indices, as well as soil permeability (related with water availability). We then extrapolated the models to predict these fox parasite diversity indices in non-sampled provinces and have a view of their geographical trends.

Prevalence of serum antibodies to canine adenovirus and canine herpesvirus in the European red fox (Vulpes vulpes) in Australia

To determine the seroprevalence and aspects of the epidemiology of canine adenovirus (CAdV) and canine herpesvirus (CaHV-1) in European red foxes (Vulpes vulpes) in Australia. Serum samples were collected opportunistically from foxes in 1991-1994 in Western Australia (WA) and South Australia (SA) and in 1980-1984 and 1990-1994 in New South Wales (NSW) and the Australian Capital Territory (ACT). The sera were examined for antibody to CAdV and CaHV-1 using ELISAs. Seroprevalence in the different regions was determined for both viruses and the CAdV data were analysed for interactions between decade of collection, age, season, region and gender using logistic regression. The overall prevalence of antibody to CAdV was 23.2% (308/1326) but was significantly higher in sera collected in the eastern states of Australia (47%: 233/498) than in WA (9%: 75/828). Overall, in NSW and the ACT, there was a significantly lower prevalence in juveniles than in adults and the prevalence in juveniles in the 1990s was significantly lower than in the 1980s. The prevalence was also significantly lower in the autumn than in the winter for juveniles but the reverse held for adults. The NSW and ACT data were subdivided into eastern (including the ACT) and western regions. This revealed a significantly higher prevalence in the winter than in the autumn for the west and the reverse in the east. In WA, the northern rangeland regions of WA had lower prevalence (1.9%) than the southern agriculture regions (10.7%). Seasonally, there was a peak prevalence in the spring dropping through the summer and autumn and rising again in the winter. This seasonal pattern was also found in the combined data for all sites in the 1990s. There was no gender difference in prevalence of CAdV either overall or in different regions. The overall prevalence of antibody to CaHV-1 was 2.2% (28/1300). The small number of positives allowed only limited statistical analysis that did not reveal any differences in decade of collection, age, season or region. CAdV infection is common in the Australian fox population whereas CaHV-1 infection is rare. For CAdV, the age and seasonal patterns of seroprevalence were generally consistent with the recruitment of young susceptible foxes into the population in the spring and the accumulation of infections with age. The differences in regional prevalences correlated with fox density. The low prevalence of antibody to CaHV-1 suggests that CaHV-1 may be a more suitable vector than CAdV for bait delivery of immunocontraceptive antigens to foxes in Australia.

The influence of predation risk on foraging behaviour of brushtail possums in Australian woodlands

The potential effects of predation risk on common brushtail possums were investigated in south-eastern Australian woodlands. Patterns of habitat use, foraging costs using giving-up density (GUD) experiments, and indices of body condition and reproductive success were examined at eight sites in two habitat types (eucalypt- or cypress-pine–dominated stands), within three areas of different red fox abundance (high, moderate and low fox density). In cypress-pine–dominated stands, possums travelled further on the ground, visited more feeding stations and had lower GUDs at feeders where foxes were removed than did possums in high-fox-density sites. In contrast, there was no effect of fox removal on the behaviour of possums in eucalypt-dominated stands. Fox removal also had no effect on indices of body condition and reproduction. Minor effects of microhabitat were detected with trackplot and GUD experiments, but, overall, the results suggest that habitat at the stand-level was more important. The non-lethal effects of foxes in different habitats may need to be taken into account when developing conservation strategies for native marsupials.

Faecal density counts for monitoring changes in red fox numbers in rural Britain

Summary Quantifying animal density is a fundamental requirement for the successful management of canid species. Faecal transects along linear features represent a cost‐effective means of quantifying relative density. However, it is unclear whether such counts can be utilized to estimate absolute density. In Britain, due to proposed legislative changes in permitted culling practices, and as part of a wider monitoring programme, the current and future density of red foxes Vulpes vulpes is of applied interest. In this study, we counted fox faeces in 444 1‐km squares throughout mainland Britain to construct a baseline index of fox density against which future changes could be measured. By incorporating estimates of the defecation rate and the proportion of scats associated with linear features, we estimated absolute density in seven landscapes. These estimates were compared with existing data on fox density. On average, captive foxes consumed 0·85 kg food day−1. Defecation rate (8 scats fox−1 day−1) was not affected by the type of food consumed. The proportion of scats associated with linear features was determined by feeding individual free‐living foxes a known amount of food containing an indigestible marker. On average, 5·7% of scats were deposited along linear features. Mean fox density in landscapes ranged from 0·21 to 2·23 foxes km−2. These estimates agreed closely with the limited data available on fox density in Britain. The total rural fox population was estimated to be 225 000 foxes (95% confidence interval 179 000–271 000). Including foxes in urban areas, the total national population is estimated to be approximately 258 000 individuals. Synthesis and applications. The results suggest that faecal density counts have the potential to be used to estimate fox density over large spatial scales, although further work on estimating the proportion of scats associated with linear features and the use of faeces in territorial marking by canids is required.

Is it possible to monitor mammal population changes from counts of road traffic casualties? An analysis using Bristol's red foxes Vulpes vulpes as an example

ABSTRACT 1. Counts of road traffic casualties (RTCs) have been proposed as one potential method of monitoring changes in the abundance of several mammal species in Britain. However, before such schemes are implemented, it is vital that the relationship between animal density and RTCs is verified and quantified. In this paper, we analyse data collected as part of a long‐term study of red foxes Vulpes vulpes in Bristol, UK to determine whether RTCs reflected changes in fox numbers. 2. Associations between fox density and RTC counts were examined using data collected from throughout Bristol during 1978–84 (spatial model) and from an intensive longitudinal study in the north‐west of the city during 1990–94 (temporal model). For both sets of data, there was a significant relationship between fox density and RTCs; in the case of the temporal model, this was only evident after the data had been manipulated by calculating running means across seasons. These regression models only explained 58% and 43% of the variance observed in the data, respectively. 3. In both analyses, there was a significant difference between the distribution of casualties and the availability of different road types; more foxes were killed on major category roads (e.g. motorways, A‐roads). Incorporating the length of each road category in each region in the spatial model improved the variance explained to 81%. This level of precision would be sufficient for a national monitoring programme. However, we were able to minimize or eliminate a number of factors that could potentially confound the use of RTCs for a national monitoring programme; these factors are discussed in detail. At present, we conclude that further investigation into the validity and precision of this technique is required for a range of mammal species before it could be used in a national monitoring programme.

Epizootiologic and ecologic investigations of European brown hares (Lepus europaeus) in selected populations from Schleswig-Holstein, Germany.

From 1997-99 European brown hare (Lepus europaeus) population densities were estimated by spotlight surveys within different areas in Schleswig-Holstein, Germany. These areas showed a wide variation in local hare population densities. In addition, red fox (Vulpes vulpes) densities were estimated in 1997 by surveys of fox dens and litters. Sera of 321 hares (shot between 1998-2000) from four study areas were examined for antibodies against European brown hare syndrome virus (EBHSV) by enzyme linked immunosorbent assay (ELISA), Yersinia spp. (n = 299) and Francisella tularensis (n = 299) by western blotting, Brucella spp. by Rose Bengal test, and Toxoplasma gondii by Sabin-Feldman test (n = 318). Tissue samples comprising lung, liver, spleen, kidney, heart, and adrenal glands were collected for histopathology. Liver (n = 201) and spleen (n = 201) samples were processed for the detection of T. gondii-antigen in tissue sections and 321 liver and spleen samples were investigated for EBHSV-antigen by ELISA. Furthermore, 116 hares were examined macro- and microscopically for lungworms. Significant negative correlations between hare and fox densities were found in spring and autumn 1997. Antibodies against EBHSV were detected in 92 of 321 (29%), against Yersinia spp. in 163 of 299 (55%), and against T. gondii in 147 of 318 (46%) hares. We evaluated the potential influence of origin and hunting season on exposure rates of hares using logistic regression analysis. A strong association between hare densities and exposure rates was observed for various agents. One hundred and eight of 201 (57%) hares were positive for T. gondii-antigen. All sera were negative for antibodies against Brucella spp. and F. tularensis and all lung samples were negative for lungworms. In conclusion, variation in red fox densities may have an impact on the hare populations examined and the infectious diseases we studied seem to play a subordinate role in the dynamics of European brown hare populations from Schleswig-Holstein.

Habitat use and diet of the red foxVulpes vulpes in an agricultural landscape in Poland

Red foxVulpes vulpes density, diet and den site selection were studied in a unwooded farmland of western Poland. During years 1999–2000 snow tracking was performed, and in 1999 dens were counted. Estimated population densities based on snow tracking were 2.1 and 1.79 individuals/km2 respectively, while den counts gave a value of 2.20 individuals/km2. Almost all dens were located on steep slopes, mainly on banks of drainage ditches (51%) and marsh banks (18%). Foxes markedly preferred southern exposure, while western slopes were avoided. The relatively high number of dens, their clumped distribution and the small number of breeding dens show that the studied population was organised in 5 clans. 26% of the dens were used only temporarily indicating that some of individuals use more than one den. Scat analyses revealed a high frequency of rodents, birds (mainly poultry) and garbage items in fox food (65.6, 47.9, 16.0% occurrence in scats, respectively). Fox adaptation to anthropogenic food sources and change in den site selection are discussed as main factors responsible for the occupation of farmland and in consequence, for the increase of fox densities in Poland.

Variability in marine resources affects arctic fox population dynamics.

Terrestrial predators in coastal areas are often subsidized by marine foods. In order to determine the potential impact on terrestrial prey, the numerical response of predators to each food source must be determined. In winter, arctic foxes (Alopex lagopus) may forage on the frozen Arctic ocean and scavenge carcasses of seals killed by polar bears (Ursus maritimus), but the importance of this food source and its effect on the population cycles of arctic foxes and lemmings (their primary prey) are unclear. I estimated the marine component of the late winter diet of arctic foxes near Churchill, Manitoba, using stable-carbon isotope analysis, and compared these estimates to abundance of arctic foxes and collared lemmings (Dicrostonyx richardsoni). From 1994 to 1997, fox density varied with lemming abundance, but following a decline, fox abundance began increasing before lemmings. During this increase marine foods were consumed more than in other years, with over two-thirds of food intake from marine sources. Arctic and red fox (Vulpes vulpes) harvests in the 1980s to 1990s were correlated with published estimates of polar bear body mass, which varies with seal productivity. However, this relationship disappeared during high lemming years. Thus, variation in marine productivity affects arctic fox abundance, especially when their primary prey are scarce, and this numerical response of arctic foxes to marine resources and lemmings suggests that increased predation by arctic foxes subsidized by seal carrion may delay the recovery of low lemming populations.

Ecology: Hunting and fox numbers in the United Kingdom.

The potential impact of fox-hunting ban in Britain is a contentious issue1 that has been explored by Baker et al.2. They conclude that a suspension of lowland fox-hunting for nine months during 2001 made no difference to fox density in certain areas. We are not confident, however, that their analysis supports their conclusions — their study does not consider statistical power or account sufficiently for regional variation, and also uses an inappropriate statistic.

The status of foxes Vulpes vulpes on the Isle of Man in 1999

ABSTRACT 1. Foxes Vulpes vulpes probably did not occur naturally on the Isle of Man, but were present in small numbers in the mid 19th century. They were introduced again in the 1980s, and in 1990 the population was estimated at 120–300 individuals (20–50 per 100 km2) on the basis of field signs. We used a nocturnal spotlight transect survey technique to assess the status of foxes on the Isle of Man in September 1999. This method had previously been used effectively to estimate fox densities in populations as sparse as 16 per 100 km2. We surveyed a total of 852 km over a period of eight consecutive nights, during weather conditions which allowed excellent visibility. No foxes were seen. 2. By comparison with equivalent survey efforts in reference areas of mainland Britain, we conclude that post‐breeding fox density on the Isle of Man was certainly below 2.5 per 100 km2, implying a maximum of 15 foxes on the entire island. We estimate a probability of only 15–25% that a fox population of 1 per 100 km2 was present but not detected; this would be equivalent to only five or six individuals on the whole island. Foxes may even be entirely absent, although unsubstantiated sightings continue to be reported. 3. This finding is significant in understanding the ecology of the Isle of Man, and in planning the conservation of a number of ground‐nesting bird species there, as well as for farming interests, and for contingency planning against an accidental introduction of rabies.

The city-fox phenomenon: genetic consequences of a recent colonization of urban habitat.

The red fox (Vulpes vulpes) is one of the best-documented examples of a species that has successfully occupied cities and their suburbs during the last century. The city of Zurich (Switzerland) was colonized by red foxes 15 years ago and the number of recorded individuals has increased steadily since then. Here, we assessed the hypothesis that the fox population within the city of Zurich is isolated from adjacent rural fox populations against the alternative hypothesis that urban habitat acts as a constant sink for rural dispersers. We examined 11 microsatellite loci in 128 foxes from two urban areas, separated by the main river crossing the city, and three adjacent rural areas from the region of Zurich. Mean observed heterozygosity across individuals and the number of detected alleles were lower for foxes collected within the city as compared with their rural conspecifics. Genetic differentiation was significantly lower between rural than between rural and urban populations, and highest value of pairwise FST was recorded between the two urban areas. Our results indicate that the two urban areas were independently founded by a small number of individuals from adjacent rural areas resulting in genetic drift and genetic differentiation between rural and urban fox populations. Population admixture and immigration analysis revealed that urban-rural gene flow was higher than expected from FST statistics. In the five to seven generations since colonization, fox density has dramatically increased. Currently observed levels of migration between urban and rural populations will probably erode genetic differentiation over time.

Predation of southern brown bandicoots Isoodon obesulus by the European red fox Vulpes vulpes in south-east Victoria.

PREDATION by European red foxes (Vulpes vulpes) has been identified as at least partially responsible for local declines of populations of many small to medium-sized mammals in Australia and is listed as a ‘key threatening process’ under the Victorian Flora and Fauna Guarantee Act, 1988 and the Federal Environment Protection and Biodiversity Conservation Act, 1999. Foxes occur in large numbers throughout urban, suburban and rural areas where they opportunistically take carrion, small to medium-sized mammals, birds, insects and fruit (Menkhorst 1995; Marks and Bloomfield 1999). They also kill poultry and larger mammals such as macropod species and sheep (Menkhorst 1995). In many conservation areas, particularly in near-urban locations where fox densities are high, they are thought to pose a serious threat to biodiversity conservation (Menkhorst 1995; Friend et al. 2001; Mahon 2001).

Home range and habitat use of the kit fox (Vulpes macrotis) in a prairie dog (Cynomys ludovicianus) complex

AbstractThe largest remaining black‐tailed prairie dog Cynomys ludovicianus towns in North America are in Mexico, where they coexist with the kit fox Vulpes macrotis, providing a unique opportunity to study the relationship between these threatened species. We hypothesized that the presence of prairie dogs would positively affect the kit fox population in our study area in north‐western Mexico, and that these influences would be manifest in home‐range size, density and habitat selection. We estimated fox densities fluctuating from 0.32/km2 to 0.8/km2, and radio‐telemetry revealed minimum convex polygon home ranges averaging 11 km2. These values are within the bounds of estimates from study sites elsewhere. Foxes used mesquite scrub less than expected, but grassland more than expected in relation to availability. Other habitats, including prairie dog towns, were used at random. Most (65.1% of 43) fox dens were in grassland, and were enlarged kangaroo rat Dipodomys spp. (34.9%) or prairie dog (34.9%) burrows. That kit foxes seemed to select grasslands rather than prairie dog towns was unexpected, particularly as prairie dogs are known to be a major component of kit fox diet. Foxes may reduce the amount of time they spend in prairie dog towns to avoid coyotes, which can be responsible for significant swift fox mortality. In our study area, coyotes were more active in prairie dog towns than in the grassland, where they were regularly shot. However, grassland used by kit foxes is a short‐lived product of prairie dog poisoning, which is quickly invaded by scrub, a habitat favoured by coyotes. We conclude that kit fox conservation initiatives in north‐western Mexico should be closely linked to conservation of the prairie dog ecosystem.

Red foxVulpes vulpes density and habitat use in a rural area of western Poland in the end of 1990s, compared with the turn of 1970s

The red foxVulpes vulpes (Linnaeus, 1758) density and habitat use were studied in open farmland of western Poland, where forests covered only 6% of the area. During 1997-2000, nocturnal spotlight counts (in spring and early winter), the location of breeding sites and snow tracking were carried out, and the feeding habitat was described based on the stomach content of shot individuals. The average fox density estimated on the ground of spotlight counts was 1.02 individuals/km2 in spring and 1.63 ind./km2 in early winter, while the winter density obtained from the results of track counts was 1.26 ind./km2. The average breeding population density, calculated as the double density of breeding sites (mean 0.31/km2), amounted to 61% of the average total spring density, which indicates the occurrence of surplus individuals in the population. The searching intensity of farmland by foxes did not changed with the increasing distance from forests, but relatively larger number of individuals was observed <0.5 km than 0.5–1.0 km away from settlements. Out of 81 identified breeding sites, 17% were located in forests and 83% in farmland. The predominant ingredients of the fox’s diet were farm livestock and small rodents (44.4 and 43.8% of the stomach content volume, respectively). The fox density in the study area was 5.4 times higher, compared with the turn of the 1970s, and changes in the habitat use consisted of more intensive occupation of open farmland and the use of human-produced food. Thus, these changes may have been among reasons of the increase in the fox density in western Poland.

Population ecology of swift foxes (Vulpes velox) in southeastern Colorado

Swift foxes (Vulpes velox) were once distributed across most of the shortgrass prairie of North America. The arrival of settlers and the concurrent loss of habitat, trapping, incidental poisoning, and shooting brought about a decline in its numbers until the swift fox remained only in the southern part of its historic range. A current understanding of swift fox population ecology is important to management and conservation efforts. We examined the population ecology of swift foxes on a native shortgrass prairie ecosystem in southeastern Colorado. From January 1997 to December 1998 we investigated home-range size and space use, spatial overlap, dispersal patterns, survival rates, and reproduction using a sample of 90 (42 males, 48 females) radio-collared foxes. Home ranges were largest (9.4 ± 4.9 km2) and spatial overlap was greatest using nighttime locations when foxes were active, while daytime locations indicated that the use of dens was exclusive among social units, and space use (2.8 ± 2.2 km2) was reduced during the day. Among resident foxes, survival rates were higher for adults than for juveniles. For dispersing foxes, adults that dispersed had higher survival rates than juvenile dispersers. Social units ranged in size from 2 to 4 foxes. About 58% of the social units produced pups; litter size averaged 2.4 pups at den emergence. Among the surviving pup cohort, some pups were philopatric, some dispersed long distances, while others dispersed to neighboring territories. Swift fox density was negatively associated with both coyote (Canis latrans) and lagomorph abundance but positively correlated with rodent abundance.

Echinococcosis in Dogs in the Czech Republic

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Demography of bridled nailtail wallabies translocated to the edge of their former range from captive and wild stock

Despite numerous, generally unsuccessful attempts to reintroduce threatened Australian mammals, the factors leading to their failure have not been fully clarified, although predator control would appear to be of paramount importance. An experimental approach was taken in attempting to establish a population of bridled nailtail wallabies in an area of apparently suitable habitat and low fox density, but on the edge of the species’ former range. The 133 wallabies released since late 1996 comprised four groups: captive-bred animals, wild caught from the single remaining wild population, animals that were captive bred and acclimatised at the translocation site in a 10 ha predator-proof enclosure, and animals which had been bred in the enclosure. Survival was highest in those bred in the enclosure and highly variable among captive-bred animals. Survival estimates for wild recruits suggested the population would maintain a positive rate of increase under prevailing environmental conditions. Spotlighting surveys suggested the population had increased to approximately 400 animals by late 1999. Above average rainfall during 1996–1999 and no apparent predation suggests caution in describing the translocation as a success. Ongoing monitoring is critical, because it is uncertain how the population will cope with drought and inevitable predation events, and whether the population will expand and persist outside of limited preferred habitat.