Natal dispersal and post-weaning survival of juvenile snowshoe hares during a cycle population increase

Juvenile snowshoe hares (Lepus americanus) in southwestern Yukon were monitored using radio telemetry to determine the effects of litter group on natal dispersal and postweaning survival. A total of 84 juveniles representing the four litter groups bom in 1995 were monitored from June 1995 to April 1996 on control areas and areas in which supplemental food was provided. Natal dispersal distance, age and date of emigration, survival rate, and proximate cause of death were examined. Natal dispersal distances (distance from nest site to site of first breeding) of hares ranged from 23 m to over 16 km. Fifty percent (9/18) of juveniles whose nest sites were known and survived until their first breeding season were classified as emigrants (dispersed a distance further than two adult home range diameters). Emigrants did not suffer significantly higher mortality than those individuals which did not emigrate. Neither dispersal distance nor the proportion of hares which emigrated differed between food addition and control areas. On the control areas, there was no evidence of sex-biased natal dispersal. However, on the food addition areas, a higher proportion of males than females emigrated and males dispersed significantly farther than females. This pattern possibly resulted from the increased population density on the food addition areas. Age at emigration varied from 31 days to 140 days, but was not related to the sex of the individuals. Food addition had no observable effect on emigration age, however there was a significant effect of litter group. Third litter juveniles emigrated at an older mean age (84 days) than first (48 days) and second (42 days) litter juveniles. Twenty-eight day survival did not differ between food addition and control areas for any litter group. Over the study period, 28-day survival of juveniles (all litters combined) did not differ significantly from adults (juveniles: 0.91, adults: 0.93). However, when examined by litter group, third litter survival was significantly lower than adult and second litter survival, while fourth litter survival was significantly lower than adult, first, and second litter survival. These differences were the result of differential survival among the litter groups during a three month period in the fall (September-November). Predation was the primary proximate cause of death for weaned juvenile hares, accounting for 86% (37/43) of deaths. Although the dominant predators of juvenile snowshoe hares were annual residents, avian predation was low after November while mammalian predation was constant from mid-August through April. No collared weaned juveniles died before mid-August.Science, Faculty ofZoology, Department ofGraduat