Neale, J. C. C. and Sacks, B. N. 2001. Resource utilization and interspecific relations of sympatric bobcats and coyotes. -Oikos 94: 236 -249.We used scat analysis and radiotelemetry to characterize use of foods and habitats by sympatric bobcats and coyotes, and evaluated these in the context of spatial and temporal relationships to assess the potential for, and evidence of, interspecific competition. Bobcats and coyotes exhibited broad and overlapping diets. However, diets of the two predators differed in the relative contributions of small and large prey, with bobcats consuming relatively more rodent and lagomorph biomass and coyotes consuming relatively more ungulate biomass. Consumption among rodent prey species was highly correlated between bobcats and coyotes, indicating no evidence of prey partitioning within this group. Habitat selection by the two predators differed slightly at the landscape scale but not within home ranges. Bobcats and coyotes occupied small, overlapping home ranges, such that the likelihood of interspecific encounters (direct or indirect) was high. Bobcats displayed slight avoidance of overlapping coyote core areas during coyote reproductive seasons (winter and spring), when coyotes are typically most territorial (toward conspecifics), but displayed slight attraction during times of year when coyotes were not engaged in reproductive activities. Relative to coyotes, which were strongly nocturnal, diel activity patterns of bobcats were more diurnal and variable. However, activity patterns were not inversely correlated. Overall, these predators appeared to use resources independently and we found little evidence of negative interactions. Differences in resource use by bobcats and coyotes appeared to relate to fundamental niche differences as opposed to competition-related resource partitioning.
Coyote (Car1i.s1ntran.s)depredation is a chronic problem for sheep producers in the western United States. Due to increasingly localized control efforts, behaxior of individual coyotes in sheep-ranching entironments is becoming a more important consideration. We radiotracked 14 coyotes on a year-round sheep-ranching facility in north-coastal California during September 1993-December 1995. Breeding coyote pairs nsed mutually exclusive territories (maximum overlap between 90% adaptive kernel home ranges = 4%).Nonbreeding coyotes xvere transient or varied in their degree of fidelity to putative natal territories but generally avoided cores of nullnatal territories. Breeding coyotes whose territories contained sheep were the principal predators of sheep. In the 1994 lambing period (1Jan-31 May), radiotelemetry indicated that 1 breeding inale was responsible for 71% of 6Ei kills. In the 1995 lanrbing period, 4 breeding pairs were strongly implicated in 92% of 48 kills and were suspected of 85% of 26 additional kills; lionbreeders were not associated with sheep depredation. Depredation was reduced only when territorial breeders known to hl1 sheep were removed. These results suggest the need for management to target breeding adults in the immediate vicinity of depredation. Efforts to remove individuals > I territory-xcidth away from problem sites are ~~nlikely to reduce depredation and may eeaacerbate the problem by creating vacancies for ne\r breeders that might kill sheep.
To investigate interspecific relationships between gray foxes (Urocyon cinereoargenteus) and sympatric coyotes (Canis latrans) and bobcats (Lynx rufus), we quantified occurrence of food items in carnivore scats and used relative abundances of scats on transects to assess space use. Dietary-overlap indices between the two canid species were high during summer and fall ([Formula: see text] = 0.89) when fruits were prevalent in scats of both species, and were lower during winter and spring ([Formula: see text] = 0.70) when fruits were less available. Foxes differed most from coyotes in their relatively less frequent ungulate consumption. Foxbobcat dietary-overlap indices were relatively low in summer and fall ([Formula: see text] = 0.37) and greater in winter and spring ([Formula: see text] = 0.74). Foxes differed most from bobcats in their more frequent consumption of fruits and less frequent consumption of lagomorphs. Abundance of fox scats was positively correlated with abundance of coyote scats during both winterspring (r = 0.52, p = 0.02) and summerfall (r = 0.75, p < 0.001) and with abundance of bobcat scats during winterspring (r = 0.59, p < 0.01) and summerfall (r = 0.22, p > 0.10). Thus, despite similarities in diet, we found no evidence that gray foxes avoided these larger predators in space.
An expanding body of research indicates that exposure to contaminants may impact marine mammal health, thus possibly contributing to population declines. The harbor seal population of the San Francisco Bay (SFB), California, has suffered habitat loss and degradation, including decades of environmental contamination. To explore the possibility of contaminant-induced health alterations in this population, blood levels of polychlorinated biphenyls (PCBs), dichlorodiphenyldichloroethylene (DDE), and polybrominated diphenyl ethers (PBDEs) were quantified in free-ranging seals; relationships between contaminant exposure and several key hematological parameters were examined; and PCB levels in the present study were compared with levels determined in SFB seals a decade earlier. PCB residues in harbor seal blood decreased during the past decade, but remained at levels great enough that adverse reproductive and immunological effects might be expected. Main results included a positive association between leukocyte counts and PBDEs, PCBs, and DDE in seals, and an inverse relationship between red blood cell count and PBDEs. Although not necessarily pathologic, these responses may serve as sentinel indications of contaminant-induced alterations in harbor seals of SFB, which, in individuals with relatively high contaminant burdens, might include increased rates of infection and anemia.
How predators select domestic relative to wild prey is of relevance to depredation management and presents opportunities to investigate foraging theory as applied to mammalian carnivores. Domestic prey have numerous qualities that should increase their energy value to predators relative to wild prey. However, whether a predator specializes on domestic prey should also depend on the relative importance of energy efficiency and nonfood‐related activities to the predator's fitness, as well as the composition of the alternative prey base. We used radiotelemetry, carcass surveys, and fecal analysis to investigate (1) whether breeding coyotes killed sheep disproportionately to sheep abundance, (2) whether coyotes consumed wild prey disproportionately to wild prey abundances, and (3) the effects of sheep abundance on consumption of five principal wild prey. Coyote pairs killed sheep in proportion to sheep abundance within territories, suggesting that coyotes did not specialize on sheep. Occurrences in scats of four small wild mammalian prey were not significantly correlated with abundance of sheep in territories, but occurrence of deer in scats was negatively correlated with abundance of sheep in territories. Small prey generally comprised a minor portion of the coyote diet. During the lambing period, consumption of deer was lower where sheep were available than where they were not and was inversely correlated over time with sheep predation rate. During the non‐lambing period, when only larger sheep were present, consumption of deer was similar where sheep were available and where they were not, and there was no significant relationship between monthly consumption of deer and sheep predation rate. Because coyotes did not specialize on sheep, lambs, or any other prey, these results suggest that their foraging strategy emphasized minimizing time spent with food acquisition over maximizing net energy gain.
How predators select domestic relative to wild prey is of relevance to depredation management and presents opportunities to investigate foraging theory as applied to mammalian carnivores. Domestic prey have numerous qualities that should increase their energy value to predators relative to wild prey. However, whether a predator specializes on domestic prey should also depend on the relative importance of energy efficiency and nonfood-related activities to the predator's fitness, as well as the composition of the alternative prey base. We used radiotelemetry, carcass surveys, and fecal analysis to investigate (1) whether breeding coyotes killed sheep disproportionately to sheep abundance, (2) whether coyotes consumed wild prey disproportionately to wild prey abundances, and (3) the effects of sheep abundance on consumption of five principal wild prey. Coyote pairs killed sheep in proportion to sheep abundance within territories, suggesting that coyotes did not specialize on sheep. Occurrences in scats of four small wild mammalian prey were not significantly correlated with abundance of sheep in territories, but occurrence of deer in scats was negatively correlated with abundance of sheep in territories. Small prey generally comprised a minor portion of the coyote diet. During the lambing period, consumption of deer was lower where sheep were available than where they were not and was inversely correlated over time with sheep predation rate. During the non-lambing period, when only larger sheep were present, consumption of deer was similar where sheep were available and where they were not, and there was no significant relationship between monthly consumption of deer and sheep predation rate. Because coyotes did not specialize on sheep, lambs, or any other prey, these results suggest that their foraging strategy emphasized minimizing time spent with food acquisition over maximizing net energy gain.
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