Effect of hibernation and reproductive status on body mass and condition of coastal brown bears

We investigated the effect of hibernation and reproductive status on change s in body mass and composition of adult female brown bears (Ursus arctos) o n the Kenai Peninsula, Alaska. This information is fundamental to understan ding nutritional ecology of wild brown bear populations. Six adult females handled in the fall and following spring (paired samples) lost 73 +/- 22 kg ((x) over bar +/- SD; 32 +/- 10%) of fall body mess over 208 +/- 19 days. Of this mass loss, 56 +/- 22% (55 +/- 22 kg) was lipid and 44 +/- 22% (43 /- 21 kg) was lean body mass. Catabolism of lipid stores accounted for. 88. 4 +/- 8.1% of the body energy used to meet maintenance demands. Overwinter differences in body composition of adult females assessed only once in eith er the fall (n = 21) or spring (n = 32) were similar to those of paired sam ples. Relative fatness of bears entering the den was positively related to the contribution of fat (%) to body mass (P < 0.01) and body energy (P < 0. 01) losses during hibernation. Thus, relative fatness at the onset of fasti ng influences the relative proportion of lipid stores and lean body mass ca tabolized to meet protein and energy demands during hibernation. In the spr ing, lone females had greater bully and lean masses than Females with cubs of the lear or yearlings. Lipid content was greatest in lone females in the fall. Studies using body mass and composition as indices of population hea lth should consider season or reproductive class.