What’s New on the Menu?

polar bear Ursus maritimus maleby Michael AW AWM1885 FracWhat’s New on the Menu?

Polar bears (Ursus maritimus) are the largest land carnivores on Earth and as such, their prey items are quite big as well. They are known to feed primarily on ringed seals and bearded seals, but have occasionally been documented hunting beluga whales and narwhals, too. These bears will occasionally scavenge on the found carcasses of other marine mammals that would be too large for them to catch such as those of bowhead, fin, grey, minke, and sperm whales. But in recent years, it has become clear that their diets are expanding, the likely cause of which is climate change.

The Arctic region is warming faster than anywhere else in the world, and the animals that live there have little choice but to adapt or perish. Due to the increasingly ice free summers, polar bears are losing the seals that are their main source of food. Polar bears hunt seals from the ice, and with sea ice cover at record lows, the bears are being forced to turn to alternative prey items on land. They expend too much energy trying to capture seals in the water, so they have begun eating huge quantities of bird eggs in an effort to supplement their diets enough to survive the warming Arctic summer until the ice returns in winter. This has had a devastating impact on the populations of certain species of Arctic birds, most notably the common eider (Somateria mollissima), a ground-nesting duck, and the thick-billed murre (Uria lomvia), a cliff-nesting bird, whose colonies are declining rapidly in close association with shrinking summer sea ice. According to Samuel Iverson, the lead author of a recent report on this subject, “A single bear can essentially devastate all the eggs on an island,” recalling an instance where he witnessed a polar bear eat its way through an entire eider colony of nearly 300 nests and 1,200-1,500 eggs within a 48-hour period. In reference to the bears eating murre eggs, Iverson says “They'll just walk right down the cliffs and work their way along the ledges and go from one egg to the next." This new bear diet has the potential to wipe out entire bird populations within one or two seasons and could eventually even lead to whole species extinction.

Last year, polar bears were also observed eating white-beaked dolphins (Lagenorhynchus albirostris), an animal that has until now never been a prey species for these bears. These cetaceans are regularly observed in Arctic waters in the late summer and early autumn, but this is the first time they have been seen in the waters around Svalbard in the early spring. The loss of sea ice and warmer temperatures make these northern waters accessible earlier in the year, and it is suspected that white-beaked dolphins were captured by polar bears when their pod became trapped in shifting ice. One of the polar bears feeding on the dolphins was even seen exhibiting a behavior called “caching” which involves covering the carcass with snow in an effort to hide it from other potential predators, and is considered to be rare in this species.

All of these novel dietary observations illustrate the changes being set in motion by our warming climate.

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