DYNAMICS OF A SNOWSHOE HARE POPULATION IN FRAGMENTED HABITAT

During November 1988-December 1991 we livetrapped, radio-collared, and monitored the survival, reproduction, and movements of snowshoe hares (Lepus americanus) in highly fragmented habitat near the species' geo graphic limit in central Wisconsin. Our 7 study areas centered on 5- t o 28-ha patches of prime habitat: dense stands of willow (Salix), alde r (Alnus), and regenerating aspen (Populus) on poorly drained soils. M aximum hare densities averaged 1.6-0.8/ha, and were unrelated to patch size. Rapid declines to extinction occurred on 3 of the 5 smallest st udy areas; on another, where extinction seemed imminent, juvenile ingr ess restored the population. On the 2 largest areas (23 -28 ha of prim e habitat) hare populations were stationary during the first 2 years, but declined by 50-70% in the third as mean annual (September-August) survival of radio-collared hares fell from 0.27 (1988-1990) to 0.07 (1 990-1991). Annual survival on the 3 extinction sites averaged just 0.0 15 compared with 0.179 elsewhere. Reproduction did not differ between small (5-7 ha) vs. larger (23-28 ha) patches nor between years. Estima ted dispersal of adult and juvenile hares from the 5 small study areas was twice as high as from the 2 larger, viz. 16 vs. 35% annually. Dis persers appeared to have markedly lower survival. Predation, chiefly b y coyotes (Canis latrans), was the proximate cause of 96% (117 of 122) of natural deaths among radio-collared hares, and was therefore the o verwhelming determinant of survival and thus population trend. Results of this study suggest that probabilities of extinction in such fragme nted habitat depend importantly on patch size and attendant hare numbe rs; i.e., fall populations of < 10 hares frequenting patches of prime habitat less-than-or-equal-to 5 ha are not likely to persist long with out ingress.