What to eat now? Shifts in polar bear diet during the ice‐free season in western Hudson Bay

• Published in: Ecology and evolution Vol. 3; no. 10; pp. 3509 - 3523
• Main Authors: Gormezano, Linda J., Rockwell, Robert F.
• Format: Journal Article
• Language: English
• Published: England John Wiley & Sons, Inc 01-09-2013; Blackwell Publishing Ltd
• Subjects: Advantages; Animal behavior; Aquatic birds; Aquatic mammals; Chen caerulescens; Chen caerulescens caerulescens; Climate change; Diet; Eggs; Fatty acids; feces; Food; Foraging behavior; Hunting; Ice; Ice breakup; Marine mammals; Nutrient deficiency; Original Research; Physiology; Polar bears; Polar environments; Predators; Rangifer tarandus; scat; Seals; Seals (animals); Spring (season); Studies; terrestrial; Terrestrial environments; Ursus maritimus; western Hudson Bay; Hudson Bay; Arctic region; PN, Arctic; PNW, Canada, Hudson Bay; Climate change; polar bears; terrestrial; scat; western Hudson Bay; diet; Ursus maritimus; feces
• ISSN: 2045-7758; 2045-7758
• DOI: 10.1002/ece3.740

Under current climate trends, spring ice breakup in Hudson Bay is advancing rapidly, leaving polar bears (Ursus maritimus) less time to hunt seals during the spring when they accumulate the majority of their annual fat reserves. For this reason, foods that polar bears consume during the ice‐free season may become increasingly important in alleviating nutritional stress from lost seal hunting opportunities. Defining how the terrestrial diet might have changed since the onset of rapid climate change is an important step in understanding how polar bears may be reacting to climate change. We characterized the current terrestrial diet of polar bears in western Hudson Bay by evaluating the contents of passively sampled scat and comparing it to a similar study conducted 40 years ago. While the two terrestrial diets broadly overlap, polar bears currently appear to be exploiting increasingly abundant resources such as caribou (Rangifer tarandus) and snow geese (Chen caerulescens caerulescens) and newly available resources such as eggs. This opportunistic shift is similar to the diet mixing strategy common among other Arctic predators and bear species. We discuss whether the observed diet shift is solely a response to a nutritional stress or is an expression of plastic foraging behavior.
We analyzed scat contents to characterize the current terrestrial polar bear diet in western Hudson Bay and compared our results to a similar study done in the 1960s to see how the diet has changed since the onset of climate‐related changes. We found that polar bears are eating new foods (eggs, caribou) in relative proportion to their availability on the landscape. We discuss whether the diet shift is solely a response to nutritional stress or is another expression of plastic foraging strategy typical of other Ursids.