As climate change melts sea ice earlier in the year, polar bears have begun hunting for meals on land like bird eggs. They are not very good at it, a new drone-based study reveals. It could be another bad sign of the bears’ ability to survive in a changing world, researchers say.
“This is a really elegant study,” said Robert Rockwell, an ecologist at the American Museum of Natural History who has studied polar bears for 50 years. He calls the team’s use of drones an “excellent” way of observing animal behavior.
To find out, University of Windsor biologist Patrick Jagielski and colleagues visited Mitivik Island. Located in Canada’s Hudson Bay, this earthworm – slightly larger than New York City’s Grand Central Station – hosts up to 8,000 ducks or eider ducks each summer. (The island’s name means “duck place” in Inuit.)
The island has also become a polar bear’s favorite. For the past 10 years, the animals – which typically hunt seals and other marine animals on sea ice – have been visiting Mitivik at the same time as the seabirds nest, in the spring and early summer. “Some people stop on the island to snack on eggs,” says Jagielski. “Polar bears are like teenagers,” Rockwell adds. “They’re always hungry.”
Behind the safety of an electric fence, Jagielski and his team launched several drones over the island in July 2017 just before the eider was to hatch. After 11 days, they had more than 16 hours of footage from about 20 polar bears.
In the beginning, the bears were more picky about which eggs they ate. They may have avoided those covered in feces, a strategy that many eider ducks use to drive predators away. But eventually the bears overcame their indecency and decimated the nests, leading to almost complete depletion of the colony.
Yet the bears were not effective hunters, the team reports today in Royal Society Open Science. The drone footage revealed that as the season progressed and fewer eggs were left untouched by the bears, the animals often wandered fruitlessly from empty nest to empty nest – suggesting that they were wasting precious energy because they could not tell far away about a nest had eggs in it.
The ultimate impact on bears and birds is unclear. On larger land areas, the bear may use even more critical energy with their inefficient egg hunting, Jagielski says.
Rockwell counteracts that his own work in the Hudson Bay Lowlands, a wetland 800 kilometers south of Mitivik Island, has shown that polar bears there appear to be very efficient egg-feeding machines. Perhs it is because they have had to deal with ice melting longer and have learned to find these chunks. He remembers seeing a bear eat 270 eggs in just 96 hours. “Our experience is that they are very methodical,” he says. “They eat one nest, then get up, look around, and go straight to the next.”
The effect on seabirds is also unclear. Although polar bears are not good egg hunters, they can eventually endanger eiders and other birds if several of them switch to an egg diet and attack multiple bird colonies. For now, only 30% of Canada’s eider colonies are visited by polar bears.
However, Mark Mallory, a biologist at Acadia University, says that as the pressure on bird colonies continues to rise, the birds will just move to other areas. In Frobisher Bay in the Canadian Arctic, he has already noticed that eider ducks have moved their nests to escape the hungry bears. “In the short term, the bear is definitely a problem,” he says. “But if you look at it for 20 years, the eider ducks will probably move around.”