Diet and Feeding Ecology of the Coyotes, Black Bears, and Bobcats in Western Virginia and Preliminary Assessment of Coyote Parasites
Although deer abundance is high throughout most areas of Virginia, parts of western Virginia, especially on public lands, have comparatively low density deer populations. Concerns voiced by sportsmen regarding declining deer numbers in this region prompted interest in research to investigate the role of predation on deer populations. The coyote (Canis latrans) is a relative newcomer to Virginia, and relatively little is known about the role coyotes play in Virginia ecosystem dynamics, including their interactions with other sympatric predators. Research studies in other areas suggest that predation from coyotes, bobcats (Lynx rufus), and black bears (Ursus americanus) may be a significant source of deer (Odocoileus virginianus) mortality, especially for fawns, and the cumulative effects of predation from these sources may also increase the potential for additive mortality in deer populations. An important consideration when comparing feeding strategies of carnivores is the relative availability of food items across the landscape. I estimated the relative seasonal availability of several potential food items in a mosaic landscape that included some areas of prescribed burning and variable timber harvest in the mountains of western Virginia between June 2011 and May 2013. I focused on 4 broad categories of food items: white-tailed deer, mid-sized mammals (raccoons, Procyon lotor, opossums, Didelphis virginiana, cottontails, Sylvilagus spp., and squirrels, Sciurus spp.), small mammals, and soft mast. I used distance sampling to estimate deer density, camera trapping techniques to estimate mid-sized mammal trapping rates and occupancy, mark-recapture techniques to estimate small mammal abundance, and vegetation sampling to estimate % cover, which I used as measures of food availability for predation. To estimate carnivore diet, I analyzed scats of coyotes (n = 334), bobcats (n = 258), and black bears (n = 107) collected monthly from June 2011 and May 2013. Additionally, I compared estimates of % occurrence to estimates of seasonal availability of deer, mid-sized mammals, small mammals, and soft mast by ranking availability of food items from 0 (unavailable) to 4 (highly available) from my monthly and seasonal food item abundance and density estimates. I then ranked % occurrence in scat on a 0 - 4 scale and compared diet rankings to food item availability where changes in rank indicate differences from the generalist diet.
Deer densities were substantially higher in Bath County (4.75 - 16.06 deer/km²) than in Rockingham County (0.17 - 3.55 deer/km²). I estimated availability of other food items only in Bath County. For mid-sized mammals, I estimated low activity as shown by constant, but low, trapping rates (#photo events/trap nights*100) of opossums, and relatively higher, constant trapping rates of cottontails. Raccoon and squirrel trapping rates were highly variable across seasons and raccoon occupancy (proportion of sites occupied) was higher in summer and fall (0.51 - 0.59) whereas squirrel occupancy was highest in October-November (0.51 - 0.53). Cottontail and opossum occupancies were higher in burned areas (0.40 - 0.57, 0.24 - 0.46, respectively), whereas raccoon and gray squirrel occupancies were higher in unburned areas (0.23 - 0.78, 0.12 - 0.58, respectively). Using program MARK I estimated high abundance and density of Peromyscus spp. in all seasons relative to other small mammal species. Densities of meadow voles and jumping mice were high seasonally in open field habitat. Densities of eastern chipmunks, red-backed voles, and Peromyscus spp. were significantly higher in burned areas relative to unburned sites. Among soft mast species, blueberries comprised the largest % occurrence. I expect a generalist predator to consume deer at a constant rate and have lower % deer occurrence in Rockingham County where deer densities are much lower. I expect seasonally constant, but low, occurrence of opossum and relatively higher, but similarly constant, occurrence of cottontail. I expect raccoon occurrence to be relatively high in summer and fall, and lower in winter. Squirrel occurrence should peak in October and November, followed by a steady decline until June. Based on availability, Peromyscus spp. should be the most commonly occurring small mammal in the diet of a generalist predator, rivaled by meadow voles (Clethrionomys gapperi) in fall and perhaps summer. I expect chipmunks (Tamias striatus) and red-backed voles to occur at constant but low rates in predator diets. I predict that various species of soft mast may occur during their respective fruiting seasons.
Deer were the most frequently occurring food item of coyotes in all months in both counties, with % biomass consumed highest in June (Bath: 60.0 - 90.9 %; Rockingham: 55.6 - 92.3%). Deer occurrence in bobcat scat peaked in June (77.54 %). In black bear scat, deer occurrence was highest in February and March (100 %), however sample sizes in these months were extremely low (n = 2, 3 respectively). All 3 predators consumed deer more than expected in June and July. In most months, coyotes consumed deer and soft mast more often than expected (1 rank higher) and they consumed deer much higher (2-3 ranks higher) than expected in January and February. While deer was a major food item in the diets of all 3 predators, it is unclear whether this observed result was caused by predation or scavenging. It is unlikely that coyotes, bears, or bobcats are preying on adult deer with high frequency. I did not estimate the availability of deer carcasses for scavenging in this study. If deer carcasses are highly available in the study area, this may explain the high occurrence of deer in carnivore scat and the lack of seasonality in coyote samples.
Mice (Peromyscus spp.) were consumed by predators less than expected based on availability, whereas squirrels and chipmunks were consumed by bobcats more than expected. Meadow and red-backed voles were consumed more than expected by both bobcats and coyotes. Mid-sized mammals occurred with expected frequency or lower in predator scats. Coyotes had the lowest diversity and variation in diet, whereas bobcat and bear diets were more diverse including seasonal use of many species. Coyotes exhibited more selectivity (based on changes, and magnitude of changes, in rankings for food item occurrence versus availability) and appear more specialized on deer in all months than bobcats.
I analyzed 203 randomly-selected coyote fecal samples using a modified Wisconsin fecal flotation technique. I identified 13 parasite taxa, 9 of which occurred with adequate frequency to permit statistical analysis. No landscape patterns or statistically significant seasonal differences were found in prevalence of parasite taxa, and only A. caninum and Eimeria spp. were significantly higher, and Cystoisospora spp. was somewhat significantly higher, in Bath versus Rockingham Counties. By comparing my data on spatio-temporal patterns of food availability to patterns in the scats of predators, we have better understanding of predator foraging strategies and can identify opportunities for targeted management to balance predator-prey dynamics with human needs and values. More research is needed on the interactions of sympatric predators in specific areas to gain further inferences regarding population-level impacts of predation on deer in western Virginia.