Abstract
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.
Highlights
Polar bears (Ursus maritimus) are the most carnivorous of the Ursids, feeding primarily on ringed seals (Phoca hispida) and less frequently on bearded seals (Erignathus barbatus) and other marine mammals while sea ice is available for hunting (Stirling and Archibald 1977; Thiemann et al 2008)
Scat sampling occurred along 160 km of coastline and adjacent inland areas of what is termed the Cape Churchill Peninsula (Rockwell et al 2011) where polar bears are known to occur during the ice-free period in western Hudson Bay (Derocher and Stirling 1990)
If the trend toward earlier spring ice breakup in Hudson Bay continues, polar bears will spend more time onshore during summer, making any foods consumed during this period increasingly important for the bears’ persistence
Summary
Polar bears (Ursus maritimus) are the most carnivorous of the Ursids, feeding primarily on ringed seals (Phoca hispida) and less frequently on bearded seals (Erignathus barbatus) and other marine mammals while sea ice is available for hunting (Stirling and Archibald 1977; Thiemann et al 2008). Polar bears are in a negative energy balance (Derocher et al 1993), reportedly surviving primarily on their fat reserves, supplementary, terrestrial foods are consumed when available (e.g., Lunn and Stirling 1985; Derocher et al 2013) This period onshore is projected to increase as warming trends keep Hudson Bay ice free for progressively longer periods each year (e.g., Stirling and Parkinson 2006). Surviving these extended periods on land without access to seals is believed to be critical to the persistence of polar bears in western Hudson Bay (Molnar et al 2010)
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