VARIATION IN REPRODUCTIVE-BIOLOGY OF MALE BLACK BEARS

We compared the reproductive biology of male black bears in two study areas at different latitudes (36 and 47-degrees-N) and with dissimilar population characteristics (hunted versus unhunted) to test two null hypotheses stemming from previous studies: 1) no regional variation ex ists in male reproductive rhythms; 2) social factors do not contribute to variation. Both hypotheses were rejected. Serum-testosterone profi les differed between the two areas, with a sharper peak associated wit h the May-July breeding season among bears in Minnesota. Bears in Virg inia and North Carolina had a longer period of elevated serum testoste rone, in apparent accordance with more prolonged breeding periods repo rted for southerly populations of black bear. In both areas, serum-tes tosterone concentrations and size of testicles decreased from the bree ding months to autumn. By December, when all bears in Minnesota were d enned, testicles had ascended into the body cavity, and serum testoste rone reached a nadir. Serum testosterone increased during late denning (February-March), and testicles of some bears became scrotal, support ing previous suggestions that the male reproductive cycle is triggered by photoperiod. However, we also observed age-specific differences in secretion of testosterone between study sites that appeared to be rel ated to the effects of differing social structures.