Hungry Polar Bears Eating Eggs, Decimating Nesting Birds, as Sea Ice Declines

The Arctic is the fastest warming region on earth. The polar bear, the iconic large mammal of the Arctic, is threatened by the warming-caused loss of Arctic sea ice because it hunts its primary prey, seals, from the ice. Climate change is forcing polar bears to change their diets from seals to bird eggs as summer sea ice retreats in the Arctic ocean. Hungry polar bears, unable to catch seals in the open Arctic ocean, have been observed devouring every egg on an island of nesting birds. One hungry bear can strip a whole island clean of eggs, devastating the bird colony's breeding season. Hundreds of hungry polar bears could have devastating effects on vulnerable bird species. Since the 1980's the depredation of common eider and thick-billed murre colonies by polar bears has increased by a factor of seven.

Polar bears may find a way to survive climate change but the results could be devastating for bird species and other animals in the food chain that polar bears substitute for seals in their diets. The effects of climate change on ecosystems will be difficult to predict because there will be a cascade of effects as large species such as polar bears adapt to changing environments.

Long-term monitoring reveals that bear incursions onto common eider (Somateria mollissima) and thick-billed murre (Uria lomvia) nesting colonies have increased greater than sevenfold since the 1980s and that there is an inverse correlation between ice season length and bear presence. In surveys encompassing more than 1000 km of coastline during years of record low ice coverage (2010–2012), we encountered bears or bear sign on 34% of eider colonies and estimated greater egg loss as a consequence of depredation by bears than by more customary nest predators, such as foxes and gulls. Our findings demonstrate how changes in abiotic conditions caused by climate change have altered predator–prey dynamics and are leading to cascading ecological impacts in Arctic ecosystems.