Age and Condition of Deer Killed by Predators and Automobiles

We evaluated the condition of mule deer (Odocoileus hemionus) and white-tailed deer (0. uirginianus) killed by mountain lions (Felti concolor), coyotes (Cants Zatrans), and automobiles from December through March, 1969-81 in western Montana. Predators killed prime-aged animals and automobiles killed (G = 41.4, P < 0.001) more fawns and old-aged animals. Fifty-three deer (90%) killed by automobiles were in poor condition, but only 2 (7%) deer killed by predators were in poor condition. Predator selectivity could not be inferred from the sample of deer killed by automobiles. J. WILDL. MANAGE. 52(2):3 16-320 The influence of predation on young and old animals and animals in poor condition is important in population dynamics. To assess selectivity, standing age structure or herd condit ion from a representat ive sample of the herd is needed. In studies that do not involve capturing and marking herbivores, hunter kills (Fr i t ts and Mech 1981) and accidental kil ls (e.g. , automobiles: Pimlott et al. [1969], Franzmann and Arneson [1976]) are commonly used to obtain data. Although the potential for bias in a sample of hunter-killed animals is often recognized (Frazer 1976, McCullough 1979, Downing 1980), less at tent ion has been paid to possible biases in accidental kills. We present age structures and condition of deer killed by predators and by automobiles in western Montana, and examine possible biases in each sample. STUDY AREA Predator ki l ls were found on mule deer winter ranges in the foothi l l s of the Bi t terroot Mountains and white-tailed deer ranges of the Swan and Clearwater valleys in western Montana. Automobi le k i l l s were co l lec ted f rom major h ighways around Missoula, Montana. Mule deer winter ranges were primarily on south-facing slopes. These areas support a foothi l ls bunchgrass habitat interspersed with Douglas-fir (Pseudotsuga menziesii)-ninebark socarpus malvaceus) and ponderosa pine (Pinus ponderosa)-Savannah vegetation types (Pfister et al. 1977). Whitetai led deer ranges were most ly in oldgrowth forests . The Clearwater and Swan rivers , interspersed with lakes, generally divide the J. Wildl. Manage. 52(2):1988 study area, and level lowlands extend to the east and west from them to meet an east-facing slope on the western edge and a west-facing slope on the eastern edge of the study area. Bunchgrass habitats of the ponderosa pine series are present in limited portions of the study area. All but 4 of the 15 habitats within the Douglas-fir series described by Pfister et al. (1977) are distributed in a mosaic pattern within the study area. The major highways where deer killed by automobi les were col lec ted ran a long r ivers be low mule deer winter ranges and through white-tailed deer ranges and agricultural lands.