Survival and Cause‐Specific Mortality of Red Foxes in Agricultural and Urban Areas of Illinois

Abstract

Range expansion and population increase by coyotes ( Canis latrans ), reduced hunting and trapping, and intensified agricultural practices in the Midwest have altered red fox ( Vulpes vulpes ) mortality, although relative impacts of these factors are unknown. We examined mortality causes and survival of red foxes in urban and rural agricultural areas of Illinois, using radio telemetry data from 335 foxes (Nov 1996 to May 2002). We used Akaike's Information Criterion to evaluate six survival models for foxes reflecting 1) environmental effects, 2) intrinsic effects, 3) temporal effects, 4) behavioral effects, 5) social effects, and 6) a global model. Environmental and intrinsic models of survival were optimal for adult foxes. Adult foxes with low (0‐20%) and high (80‐100%) percentages of row crops in their home ranges had higher survival than adults with moderate percentages (40‐70%). Heavier adults at capture also survived better. A global model (all covariates) was optimal for juvenile foxes. Higher juvenile survival associated with larger litters, lower body fat, and reduced dispersal time. Yearly survival ranged from 0.18 for rural male juveniles to 0.44 for rural female adults. Adult survival rates (0.35) were 11% higher than juvenile survival rates (0.24). Yearly survival varied for urban foxes due to cyclic outbreaks of sarcoptic mange ( Sarcoptes scabei ). Thus, summer survival (May‐Sep) of urban juveniles ranged from 0.10 (mange present) to 0.83 (no mange recorded). M…