DENNING CHRONOLOGY OF FEMALE BLACK BEARS - EFFECTS OF FOOD, WEATHER, AND REPRODUCTION

We studied factors affecting the chronology of denning by 104 female b lack bears (Ursus americanus) from three areas in Maine from 1982 to 1 988. At two areas in northern Maine, entry into dens followed an alter nate-year pattern with most bears denning in mid to late October when beechnuts (Fagus grandifolia) were scarce, and in mid to late November the next year when nuts were abundant. This pattern may have occurred for greater-than-or-equal-to 11 years and has not been reported previ ously for a black bear population. From 1986 to 1988, patterns of habi tat use reflected another behavioral response to beechnut crops; bears used hardwood forests more during autumns when nuts were abundant. An nual variation in den entry was not strongly associated with weather p atterns during autumn. Where beech trees were less common in central M aine, den entry and habitat use varied less among years. Pregnant fema les tended to den earlier than other females. Den emergence was simila r among reproductive classes, generally occurring during April within 7 days of the final snow melt. Denning periods for individuals ranged from 134 to 197 days. We concluded that black bears generally remain a ctive in autumn until a negative energy balance occurs, but we hypothe sized that pregnant females may den after they store adequate fat rese rves for reproduction.