polar bear with birds flying aboveA new study says that switching from eating seals to a lower-calorie diet of eggs won’t suit polar bears coping with climate change. Photo by Evan Richardson

Egg diet no replacement for seals as polar bears battle climate change, study finds

A switch from eating seals to seabird eggs does not provide enough energy to sustain polar bears as a warmer climate has Arctic ice melting earlier in the year, says new research from scientists at the University of Windsor and Environment and Climate Change Canada.

Their study, published in the journal Global Change Biology, predicts that continued sea ice decline combined with the bear’s new diet will have serious impacts on seabirds but the eggs still won’t be enough to improve the condition of polar bears.

“Historically, polar bears would use ice as a platform to hunt seal pups during the spring, but now that sea ice break-up is occurring so much earlier, they are forced ashore onto areas where seabirds are nesting,” says Cody Dey, lead author of the study and a postdoctoral researcher under professor Christina Semeniuk at the Great Lakes Institute for Environmental Research. “As a result, polar bears are eating thousands of seabird nests each year, and the number is increasing as climate warming progresses.”

Dr. Dey’s research draws on long-term data sets of Environment Canada going back to the 1950s, satellite ice data, field studies, Inuit ecological knowledge, and integrates these components into cutting edge computational-intelligence models in Dr. Semeniuk’s predictive-ecology lab.

“This research, alongside other recent studies, is among the first evidence of climate change affecting predator-prey relationships in the wild,” Semeniuk says. “It showcases the increasingly relevant scope of the University of Windsor’s environmental research institute, not only within the Great Lakes, but to other vulnerable aquatic ecosystems in Canada.”

One of the seabirds that is most affected is this Arctic ecosystem is the common eider. These large ducks nest in groups on small Arctic islands, and have no defense if a polar bear swims ashore and onto their colonies.

To study the interaction between polar bears and common eiders, Dey travelled to Baffin Island and worked with local Inuit from the community of Cape Dorset.

“Inuit are very in tune to this type of environmental change because they hunt eiders for meat, and collect eggs and feather down from their nests,” Dey says. “Our research suggests that eiders might nest in different locations to avoid bear predation, which could make it harder for local people to harvest eiders.”

To further understand the relationship between polar bears and common eiders, Dey used data from his field studies to build computer simulation models. These models predict that polar bear predation of eider nests will continue to increase over the next 25 years, and that a large percentage of eider nests will be consumed by polar bears during years with earlier sea ice melt.

The models also predicted that polar bears will get skinnier over time, even though they are eating more eider eggs.

“When the sea ice melts, polar bears are forced to fast until it freezes up again. Even if bears are eating eider eggs, they probably can’t meet their caloric demand because eider eggs are relatively low in calories (compared to seals),” Dey says. “Our models suggest that polar bears can’t compensate for the loss of ice-based hunting opportunities by consuming eider eggs.”

Dey plans to extend this research by investigating how polar bear predation will affect common eider populations: “Some eider colonies are being decimated year after year by polar bears. This will clearly have some consequences for the eiders, but we don’t know the exact effects yet.”

Read the entire paper: http://onlinelibrary.wiley.com/doi/10.1111/gcb.13499/epdf.