Is climate change affecting the foraging habits of eider duck predators in the Canadian north?

It took a bird’s eye view to better understand who is eating the eider duck eggs on East Bay Island in Nunavut.

Andrew Barnas, a former post-doctoral fellow in integrative biology professor Christina Semeniuk’s lab, says because of climate change, melting Arctic sea ice is pushing polar bears onto land earlier in the year. As it turns out, this phenomenon is creating the perfect conditions for predatory gulls to get access to the duck eggs.

“As the bears walk through the colony, they’re scaring eiders off from their nests leaving the nests unprotected, and gulls can come in and scoop up eider eggs,” says Dr. Barnas.

“People have seen this before, but we didn’t have the tools to dig into the idea. Now using drones to get high-quality data is something you couldn’t quite get at before.”

Barnas studied unique drone footage collected by former members in Dr. Semeniuk’s lab, Cody Dey and Patrick Jagielski, in collaboration with Environment and Climate Change Canada.

“Patrick and Dr. Semeniuk used drones to record videos of polar bears foraging on East Bay Island for common eider nests. They originally wanted to know how bears eating duck eggs was contributing to the bears’ caloric deficit.”

It was that polar bear research that drew him to work in Semeniuk’s lab. Barnas started his post-doctoral fellowship in 2020, but because of the pandemic he was unable to collect fresh footage. He used Jagielski’s original recordings to push the research further.

“They had this data and footage and I wanted to know what the gulls were themselves doing — I got to work on that same footage but this time from a bird’s perspective,” he says. Barnas and undergraduate student Cassandra Simone reviewed the footage to see what gulls were doing during polar bear foraging.

“I was really interested in these gulls and if bears are creating foraging opportunities for gulls that they wouldn’t otherwise have had.”

Barnas’ findings were recently published in the journal Ecology and Evolution.

Eiders, says Barnas, are big heavy football-shaped ducks and that are well adapted to sitting on their nests and not moving for very long periods of time.

“The gulls can’t get at these eggs unless eiders are off their nests and bears are this new disturbance source for eiders.”

“Bears want to spend as much time as they can on sea ice but as things get warmer, that ice melts earlier and forces bears onto shore more often. It is definitely happening earlier and more frequently.”

Barnas says it is highly likely this is happening in other eider populations but notes this particular population has been getting hammered every year by polar bears leading to low nest success by the eiders.

“I personally think this is impactful because it gives us a broader understanding of the effects of climate change on animal behaviour, and it paints a picture of the complex interactions that bears have in this ecosystem,” he says.

“More directly it has implications for estimating the energetic contribution of eating the eggs to bear diets. Because it might be the case that they’re not getting as many eggs as we think they are.”

Essentially, says Barnas, the bears are causing the nests to fail, but they’re just not getting the benefit from it.

“Throughout the season as there are fewer and fewer nests available, bears get more and more inefficient at finding nests. They’re revisiting old nests or not finding the same numbers they would earlier in the season and if those nests are depleted earlier in the season by gulls.”

Barnas is now a postdoctoral fellow in the Applied Conservation Macro Ecology Laboratory at the University of Victoria.