Behavior of polar bear (Ursus maritimus) cubs post-den emergence at the Detroit Zoo

In the wild, female polar bears (Ursus maritimus) with cubs may spend extended periods of time within the den following initial emergence. As a result, studying behavioral development of cubs at the denning site has been difficult and unreliable. Although care staff at zoological institutions have easier access to animals, every effort is made to minimize intrusions to maternal groups, which presents research limitations. Detroit Zoological Society staff used audio-equipped cameras installed in behind-the-scenes spaces to conduct approximately 9 weeks of monitoring on two female polar bear cubs of the same litter, one of whom (Laerke) was hand-reared while the other (Astra) was mother-reared. Monitoring spanned ages 14-24 weeks and consisted of 12, 5-min focal observations per observation day timed to evenly cover the entire 24-h day. Using generalized linear mixed models, we examined relationships between behavior and time of day, hour, and age. We also conducted descriptive analyses and used these to draw comparisons between the two cubs where appropriate. Despite different rearing environments, both cubs had highly comparable patterns of inactive, locomotory, and independent play behaviors. Astra generally decreased time spent nursing and in proximity to Suka as she aged. Data presented here represent a continuation of previous neonatal observations conducted on Astra, adding to the minimal body of knowledge currently available on first year polar bear cub development. We also report successful mitigation of stereotypic behavior in Laerke. Further studies of captive maternal groups can provide insight into this critical developmental stage, supporting both captive-based breeding efforts and in situ conservation efforts.