Behaviour and characteristics of mating polar bears (Ursus maritimus) in the Beaufort Sea, Canada

Abstract

The dynamic sea ice habitat of polar bears (Ursus maritimus) influences their mating behaviour because it makes the distribution of mates unpredictable. Pronounced sexual dimorphism of polar bears likely results from a polygynous mating system, where intrasexual competition between males influences reproductive access to females. We examine aspects of the mating behaviour of polar bears in the Beaufort Sea, Canada, from 1970 to 2014 based on 135 breeding pairs observed from March through May. Mean age of paired females and paired males was 9.7 and 11.5 years, respectively. Paired males were older (by 2.2 years) and had significantly higher mass (71 kg) than unpaired males suggesting a polygynous mating system in which larger, dominant, and potentially experienced males monopolise access to females. Our binomial logistic regression suggested age was the most important factor in predicting pairing in males, which can be explained by the correlation between age and body size. Paired females had significantly higher labial development than lone females, suggesting that labial swelling is heightened during mating. Taken together, these observed characteristics suggest a polygynous mating system in polar bears, providing further insight into potential mating system variation across their range.