Black bear reproductive rates in Yosemite National Park

Reproductive rates of nuisance black bears, Ursus americanus, in Yosemite National Park were examined from 1974 through 1988, concurrent with an effort by the National Park Service to reduce the availability of human-provided foods. Summer litter size averaged 1.6 cubs in the wilderness areas and was stable through the 15-yr study. Litter size in developed portions of the park declined from 2.0 cubs, among the highest reported for a western black bear population, to 1.3 cubs, the lowest reported. Age of first reproduction for females in developed areas was 4.1 yr. The proportion of females accompanied by summer litters averaged 0.33 in wilderness and 0.42 in developed areas. The estimated average interval between litters for females in developed areas was 2.1-2.4 yr. Overall reproductive rates did not differ between management areas and did not decline through the study period. Reproductive rate declined with increased adult female age. Reproductive parameters of females captured in wilderness were typical of a western black bear population. Reproductive parameters of females using developed areas appeared high throughout the study, suggesting that they had continued access to nutritious human food. The decline in litter size coincided with installation of bear-proof food storage lockers in developed campgrounds and may suggest the beginning of a reduction in nutrient availability.