REPRODUCTIVE-BEHAVIOR OF MALE WOOD BISON IN RELATION TO PROGESTERONE LEVEL IN FEMALES

In mammals, estrus commonly is identified by the behavior of males. Ho wever, the reliability of this indicator may vary with age or experien ce of males. We monitored fecal-progesterone levels in female wood bis on (Bison bison athabascae) that were tended. Males tended females mor e often when females were close to estrus (fecal-progesterone levels < 1 mug/g feces). Subadult males also tended females that were clearly n ot in estrus (progesterone levels >1 mug/g feces). In contrast, in an experimental population from which we removed mature males, subadults tended females in estrus longer than those not in estrus. Our results suggest that although tending behavior of males is a reliable indicato r of the occurrence of an estrous cycle, the behavior of only dominant individuals is meaningful. Subadult males often tend anestrous female s because young males are excluded from breeding by the more dominant, mature males, not because of a lack of experience. When investigating the relationship between male behavior and the female's ability to pr oduce young, as determined by subsequent births, we found that lactati ng females were more likely to ovulate than nonlactating females; but, among ovulation females, lactating and nonlactating females did not d iffer in their probability of producing young. This finding suggests t hat reproductive status of a female affects mostly ovulation, not conc eption. Accordingly, males did not prefer to tend ovulating females of either reproductive status.