Seasonal patterns in physiology and nutrition of black bears in Great Dismal Swamp, Virginia – North Carolina

Abstract

Diet quality, condition indices, and blood chemistry characteristics were determined for a black bear (Ursus americanus) population in the Great Dismal Swamp on the Atlantic Coastal Plain. Blood samples from 122 captures of 99 bears were analyzed. Seasonal shifts in diet composition were similar to previously reported findings for black bear food habits in the southeastern United States. Three major levels of diet quality were observed in terms of crude fiber, fat, and protein. Spring diets were high in protein but moderate in crude fiber. Condition indices (body weight, length/weight ratios) peaked in spring and late fall and were low during summer. Several blood characteristics (e.g., total protein, albumin, hematocrit, hemoglobin, and red blood cells) showed a similar annual rhythm (P < 0.01) for both sexes. Serum creatinine concentrations also varied seasonally (P < 0.001), with a peak during denning and high levels in spring and late fall, perhaps resulting from transition from and to hibernation. Urea/creatinine ratio was not a good indicator of the hibernating state, as 39 of 120 (32.5%) trapped bears had urea/creatinine ratios ≤ 10. Creatinine and total protein were the best indicators of the hibernating state. Albumin, hematocrit, hemoglobin, and red blood cells were the best indicators of condition during active stages, as correlations of condition indices and blood variables indicated significant (P < 0.1) associations between body condition and albumin, hematocrit, hemoglobin, and red blood cells. Nine blood variables varied with age (P < 0.1). Multivariate analysis of variance and discriminant function analysis using blood variables failed to reject the hypothesis that bears cycle through four metabolic stages throughout the year. Our results showed that metabolic shifts were tied to concomitant seasonal changes in diet quality, diet composition, and body condition. Comparison of our work with other published data on bear biology suggests that seasonal changes in bear physiology may be due partly to an endogenous rhythm.