Prey Selection and Fat Deposits of Bobcats (Felis rufus) during Autumn and Winter in Maine

Abstract

Differences in food habits among age, sex, and weight classes of bobcats have been observed (Fritts and Sealander, 1978; Litvaitis et al., 1984). These differences may reduce intraspecific competition and influence the physical condition of bobcats, especially during periods of prey scarcity or environmental stress. Competition and environmental stress may be pronounced at the northern edge of the range of the bobcat where prey may be limited and winters are severe. The objectives of our study were to determine prey use by bobcats during autumn and winter in Maine, examine bobcat fat deposits during that period, and evaluate the relationships of those parameters to age, sex, and weight of bobcats and to winter severity. Skinned bobcat carcasses (n = 230) were obtained from trappers and hunters throughout Maine during the 1980-81 through 1983-84 harvest seasons (October-February). We recorded the sex and weight of each carcass and estimated the unskinned weight using regression equations (Miller, 1980). Carcasses were then separated into weight classes according to unskinned weights ( 12 kg). Juveniles were identified by the presence of an open apical root foramen in a lower canine. Cementum annuli counts were used to distinguish yearlings from older animals (Crowe, 1975). Visceral fat deposits, including kidney and intestinal fat, were examined to evalute physical condition of bobcats. Each carcass was assigned a numerical rank of fat abundance from 0 to 3, where 0 = no fat and 3 = large fat deposits. To reduce observer variation, the same individual examined the fat deposits of all carcasses. Gastrointestinal tracts were removed and contents separated. Prey remains were identified using a reference collection of hairs, hair scale patterns, and skulls. The frequency of occurrence of each item was based on the presence or absence of the prey item in each carcass. The numeric ranks of visceral fat abundance were compared to sex, age (juvenile, yearling, adult), and weight class. Fat abundance also was compared to a winter severity index (WSI), where: