Observations of aggregating behaviour in adult male polar bears (Ursus maritimus)

Abstract

Polar bears (Ursus maritimus) are usually considered a solitary species, but between 50 and 60% of the adult male polar bears captured on land during the ice-free period in western Hudson Bay were sighted in aggregations with a mean size of 4 and a range of 2–14 individuals. The mean weight of aggregating adult males was significantly greater (approximately 60 kg) than the mean weight of nonaggregating adult males, but there were no significant differences in the mean age. Aggregations occurred throughout the ice-free period (August–October) and were most common at prominent points along the coast or nearby islands. Some locations were used over several years. The lack of competition for food and the absence of breeding activity during the ice-free period produce conditions that may facilitate aggregating. Familiarity with conspecifics may yield benefits by reducing the severity and frequency of competition for resources on the sea ice.