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Mississippi State University

Gray Fox (Urocyon cinereoargenteus)

Survival and Mortality


Results

We used 37 adult gray fox (17 males, 20 females) to estimate survival and mortality patterns. Of 18 known mortalities, 6 (33%) were attributed to human-related factors, 4 (22%) were from natural factors, and 8 (44%) were from unknown factors. Two of 8 unknown deaths occurred near distemper-killed individuals, thus canine distemper was likely causal. All canine distemper occurred during 1992. Seven (19%) gray fox experienced radio failures and were censored on the last day of observation. Four (11%) gray fox dispersed and radio contact was lost after those animals left the study area.

Annual survival did not differ between sexes (P = 0.739). Similarly, annual survival did not vary across years (P = 0.898). We detected differences (P = 0.003) in survival between breeding-denning (0.71) and whelping-pup rearing (0.89). Similarly, survival differed (P <0.001) between breeding-denning and fall-winter (0.71). However, we detected no differences (P = 0.197) in survival between whelping-pup rearing and fall-winter.

For gray fox, patterns of mortality did not differ across years (P = 0.99), between sexes (P = 0.554) or across seasons (P = 0.143). All mortalities resulting from canine distemper occurred during 1992. In 2 instances, post-mortem deterioration prevented necropsy of gray fox recovered near distemper-killed individuals. We suggest that canine distemper was likely causal in these instances. Only females were taken by hunters with all deaths occurring during the breeding- denning period, coinciding with spring turkey hunting season. Half (50%) of unknown deaths occurred during the breeding-denning season.

Summary

Although annual survival of gray fox varied considerably among years on TWMA and GP, long-term survival was consistent with previous studies in the southeastern United States. Legal trapping of gray fox did not occur on TWMA or GP, thus cause-specific mortality agents differed slightly between this study and others. We observed coyote depredation of gray fox, indicating that coyotes do prey on gray fox. Canine distemper affected gray fox populations during 1992. Although localized outbreaks of canine distemper have occurred in subsequent years, no confirmed deaths of gray fox have resulted. Gray fox are known predators of nesting and brooding wild turkey hens and turkey hunters appeared more likely to shoot gray fox than deer hunters. Thus, the probability of incidental harvest for gray fox may be a function of seasonal user group.

Differences in seasonal movement and activity patterns likely caused differing probabilities of incidental harvest across seasons. Gray fox activity rates on TWMA and GP are often higher during denning and kit-rearing periods coinciding with spring turkey hunting seasons. Gray fox activity during diurnal periods increases susceptibility to incidental harvest, particularly around den sites. Two females were shot near their den sites; both were confirmed as having kits. Incidental harvest of females may contribute to reduced recruitment through elevated juvenile mortality.

The canine distemper outbreak in 1992 affected gray fox and raccoon populations resulting in annual survival of 0.0 for radio-marked gray fox. Subsequent trapping efforts in 1993 resulted in 1 gray fox captured in 3498 trap-nights. Thus, it appears that gray fox populations did not rebound until 1994. Previous studies have documented similar impacts of canine distemper, suggesting that epizootic outbreaks that produce drastic reductions in local canid populations may require 1 to several years for recovery.