Gary L. Alt

Date of Graduation


Document Type



Many aspects of female black bear reproductive biology and early development of cubs have remained poorly documented, particularly for wild populations. Black bears were studied from 1974 through 1989, in northeastern Pennsylvania, to establish base line data for times of breeding and parturition, gestation length, characteristics of cubs at birth, cub growth and development, and cub sex ratios. Reproductive performance of females was also documented, including minimum breeding age, interbirth interval, reproductive efficiency, and litter size. Breeding activity ranged from 18 May to 12 September but peaked from mid-June through mid-July, based on 47 females captured while in estrus and 2 observed matings. Parturition occurred between 1 and 27 January, and averaged 15 January, based on 122 dates of birth. Gestation length of 15 females averaged 206 days and ranged from 169 to 248 days. Thirty-three neonates ({dollar}\\leq{dollar}3 days old), from 10 litters, were examined to determine characteristics of cubs at birth. Newborn cubs averaged 363.7 g (range 293-453) while parturient females averaged 101.2 kg (range 82.1-115.2). Age of cubs can be predicted from birth until about 50 days, based on a strong correlation between hair length and cub age. Cub weights during March were heavier for males, lighter for first litters, and inversely related to litter size. Sex ratios of 615 cubs did not deviate from parity, nor did they conform to any adaptive theories concerning age or condition of their mother, litter size, or annual variation. Minimum breeding age was determined for 34 monitored females: 1 (3%) bred at 1{dollar}1\\over2{dollar} years of age, 28 (82%) at 2{dollar}1\\over2{dollar}, 3 (9%) at 3{dollar}1\\over2{dollar}, and 2 (6%) at 4{dollar}1\\over2{dollar}. Ninety-seven percent (156 of 161) of potentially pregnant adult (age 5+) females gave birth. Litter size averaged 3.0 (range 1-5) for 211 litters tagged while 2-3 months old. Litter size was correlated with both weight and age of mother. Heavier, older females gave birth to larger litters. Females began breeding at earlier ages, produced offspring at shorter intervals, and gave birth to larger litters than for other locations reported in the literature. Estimated maximum sustainable mortality, to maintain a stationary population, between 11 and 17 percent for most black bear populations, was 25 percent for northeastern Pennsylvania, where fecundity may represent the biological maximum for the species.