Polar bears may thrive on snow goose eggs: study

Melting sea ice in western Hudson Bay may drive hungry polar bears to shore just in time to feast on snow goose eggs, says a new study. (PHOTO BY JANE GEORGE)

As climate change warms the western Hudson Bay and melts sea ice earlier in the spring, polar bears now come on shore earlier to look for food.

And, as the date of ice breakup moves up in the future, there will be even less time for polar bears to feast on ringed seal pups.

But these polar bears won’t go hungry, suggests a new study published in the on-line journal Oikos: they’ll be eating snow goose eggs.

The same climate shift causing the ice in western Hudson Bay to melt earlier means polar bears will arrive on shore just at the time when there are thousands of snow goose eggs for the taking.

And, as polar bears begin foraging on eggs, their success in finding these eggs and the numbers they eat may increase as they become better egg-hunters, the study predicts.

These easily foraged goose eggs will provide at least some of the earlier arriving polar bears with the energy needed due to the lost seal hunting opportunities, says the study, which uses models to answer the question “can polar bears reduce the abundance of nesting snow geese in western Hudson Bay?”

The answer appears to be a resounding yes.

The study, led Robert Rockwell at the American Museum of Natural History, concludes that, by eating snow goose eggs, polar bears will also help control the numbers of these birds, whose population has been growing along southern Hudson Bay near Churchill.

For now, there are only two days when polar bears are on shore at the same time when snow goose eggs are abundant, but this overlap could increase to 12 days in 25 years.

But the study’s authors say that even the most catastrophic predation rate by polar bears is not expected to eliminate the local nesting population of snow geese. That’s because the timing of the bears’ arrival and the egg laying won’t overlap every year.

So the numbers of snow geese will go down, but not enough to hurt the population which poses a threat to Arctic landscapes, they say, noting that “increased climate-driven polar bear predation could actually aid in attempts to lower snow goose abundance and reduce local habitat damage.”

“Increased polar bear predation of snow goose eggs would serve as a novel form of ‘top–down’ regulation, operating to reduce the local snow goose population,” the study’s authors say.

The study’s results also suggest that mismatches caused by climate change— that is, when climate changes also produce changes in the dependent relationships between animals— are not all “bad.”

This study makes use of data on snow geese and polar bears found in and around Wapusk National Park, about 30 kilometres east of Churchill, Manitoba.

Snow geese can be found along 150 km of coastline on the Cape Churchill Peninsula and up to 15 km inland although most nest within five km of the coast.

In other regions, polar bears have increasingly been observed eating eggs when their onshore arrival overlaps the incubation period for eggs.

Similar goose egg predations have been observed on Southampton and Coats Islands in Nunavut’s High Arctic, on Akimiski Island in southern James Bay and on Norway’s Svalbard islands.

In 2004 on southern Southampton Island, a well-nourished adult female polar bear wandered from nest to nest in a snow goose colony, scooping up the entire contents of each nest.

And in 2006 on Coats Island, biologists counted five polar bears in a goose nesting area, where they proceeded to eat the entire contents of each nest, before they walking on to the next.

Polar bears usually draw on their stored fat throughout the ice-free period.

But if they’re hungry, they may also feed on grasses, marine algae, berries, carrion, remains from human hunting, as well as occasional caribou, fish, rodents and birds.

Some biologists maintain egg eating won’t take polar bears very far because it takes too many eggs to fill a bear.