The reproductive biology and behavior of the sun bear Ursus malayanus

Few studies on the reproductive biology of the sun bear Ursus malayanus have been conducted. The current study combined hormonal profiling of female sun bears with vaginal cytology, genital appearance scoring and behavioral observations to describe the estrous cycle of the sun bear. The use of multiple techniques provided a more complete picture of the cycle than was previously available. Documenting the relationships among these measures helped create easier, less expensive options for reproductive monitoring of this species. Subjects consisted of the entire captive North American population of the subspecies Ursus malayanus euryspilus on loan to US zoos from the Malaysian government for a new captive breeding program. Profiles from the various measures suggested a gradation in strength of reproductive cycling among the female sun bears in this study. It was determined that sun bears are not induced ovulators. Neither copulation nor male presence was required for a female to ovulate; however, a male may influence the cycle. The direction of a male's influence was related to the nature of his behavioral interactions with the female. Partner females appeared to lower hormone levels via agonistic behavior. The timing of estrous cycles and patterns of hormone fluctuations in male and female sun bears along with the timing of past captive births all suggested that this species does not show reproductive seasonality. Although sun bears in this study showed pseudopregnancy, like other bears species, they are unlike other bears with respect to many of their reproductive strategies. The ecology of the sun bear, specifically living in an environment in which food is not predictably available, was proposed as an explanation for their lack of similarity with other ursids.