Vol.:(0123456789) 1 3 Polar Biology (2019) 42:919–929 https://doi.org/10.1007/s00300-019-02485-5 ORIGINAL PAPER Behaviour and characteristics of mating polar bears (Ursus maritimus) in the Beaufort Sea, Canada B. A. Biddlecombe 1  · A. E. Derocher 1  · E. S. Richardson 2  · I. Stirling 3 Received: 29 June 2018 / Revised: 12 December 2018 / Accepted: 12 March 2019 / Published online: 20 March 2019 © Springer-Verlag GmbH Germany, part of Springer Nature 2019 Abstract The dynamic sea ice habitat of polar bears (Ursus maritimus) infuences their mating behaviour because it makes the dis- tribution of mates unpredictable. Pronounced sexual dimorphism of polar bears likely results from a polygynous mating system, where intrasexual competition between males infuences 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 signifcantly 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 regres- sion 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 signifcantly 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. Keywords Polar bear · Ursus maritimus · Mating behaviour · Beaufort Sea · Sexual dimorphism · Polygyny Introduction Mating systems are infuenced by the spatial and temporal availability of females as mates for males, and female access to resources such as food (Shuster and Wade 2003; Hamel et al. 2010; Weir et al. 2011). Polygynous mating systems are common in mammals and can promote the evolution of sexually selected traits that allow for the monopolisation of females via male displays or male–male competition (Orians 1969; Shuster and Wade 2003; Bissonnette et al. 2011). In large mammals, the degree of polygyny is afected by male size, competitive ability, female movement, and in some spe- cies, individual territoriality (Poerschmann et al. 2010; Plard et al. 2011). Most ursids have polygynous mating systems, are sexually dimorphic, and use overlapping home ranges that vary with sex, age, and habitat (Stirling and Derocher 1990; Mace and Waller 1997; Kennedy et al. 2014). Polar bears (Ursus maritimus) also use overlapping home ranges, but they are much larger and infuenced by both spatial and temporal variation of sea ice and access to prey in their prime habitat, the sea ice over the continental shelf where seals are most abundant (Stirling et al. 1993; Pilfold et al. 2014; McCall et al. 2015). Polar bears in the Beaufort Sea feed primarily on ringed seals (Pusa hispida) and bearded seals (Erignathus barbatus) which vary in abundance, dis- tribution, and availability between years, as a consequence of changing sea-ice dynamics (Stirling and Archibald 1977; Smith 1980; Stirling 2002; Iversen et al. 2013; Nguyen et al. 2017). Interannual variation in the annual sea ice results in * B. A. Biddlecombe bbiddlec@ualberta.ca A. E. Derocher derocher@ualberta.ca E. S. Richardson evan.richardson@canada.ca I. Stirling ian.stirling@ualberta.ca 1 Department of Biological Sciences, University of Alberta, Edmonton, AB T6G 2E9, Canada 2 Wildlife Research Division, Science and Technology Branch, Environment and Climate Change Canada, 123 Main Street, Winnipeg, MB R3C 4W2, Canada 3 Department of Biological Sciences, Environment and Climate Change Canada, University of Alberta, Edmonton, AB T6G 2E9, Canada