REPRODUCTIVE-BIOLOGY OF FEMALE BLACK BEARS IN RELATION TO BODY-MASS LN EARLY WINTER

We examined the influence of body mass in early winter on litter size, growth and sex ratio of young, as well as the influence of gestation and lactation on overwinter loss of mass among female black bears (Urs us americanus) in La Mauricie National Park, Quebec, Canada. All adult females weighing greater than or equal to 77 kg gave birth and no fem ale reproduced when weighing <56 kg. Litter size (two to four young) w as influenced by maternal condition in early winter, and overwinter lo ss of mass greater for females producing litters of three and four you ng. For a particular litter size, heavier females tended to produce mo re male young than expected from an equal sex ratio. Maternal conditio n, however, could not explain the strongly male-biased sex ratio (2.5 males:1.0 female) at birth observed in this population. Significance o f sex ratio at birth in relation to the regulation of the population o f bears at La Mauricie National Park is discussed.