Polar bears may adapt to an ice-free Arctic, but they’re not safe from climate change, says scientist
Polar bears have become an emblem of climate change.
Their snow-white coats and Arctic habitat — and even the name itself — are synonymous with the ice that covers one-tenth of the Earth’s surface.
And that ice is disappearing.
Kingdom of the Polar Bears, a two-part documentary from The Nature of Things, is a journey into a vanishing land, following these great white bears into some of the harshest environments on the planet. Relying on vast expanses of ice to hunt for seals, polar bears have been singled out as a species threatened by warming climates. 2020 was tied for the hottest on recordaccording to data from NASA.
No ice means no hunting ground for seals — and presumably, not enough for these apex predators to eat.
But the full story of polar bears is much more complicated than that.
‘Thousands of years in an ice-free world’
Firstly, polar bears have a history of surviving extended periods without ice.
Over the years, studies have varied on pinpointing when polar bears genetically split from North American brown bears — up to 130,000 years ago according to mitochondrial DNA, some 600,000 years ago according to nuclear DNA, or as many as five million years ago from a full-genome study.
Biologist and ecologist Robert Rockwell says for the 130,000-year estimate, which coincides with the Eemian interglacial period, there was no ice in the Arctic at all.
“[Polar bears] went through a long period of several thousands of years in an ice-free world,” Rockwell says. “There were polar bears, but they weren’t on ice. They were just in the North.”
Secondly, Rockwell points out that polar bears already find food on land — every single summer. Kingdom of the Polar Bears shows Rockwell monitoring bears as they raid eggs from duck nests.
“The eggs in an eider [duck] nest is the same as 1.5 Big Macs,” he says in the documentary. “And in 96 hours, he ate 280 of those. And I worked out that that was 25 per cent of the annual energy budget that’s required for a sub-adult polar bear.”
Polar bears may adapt to a warming Arctic: Kingdom of the Polar Bears
Arctic ecologist Robert Rockwell describes how Polar Bears are adapting their diet to a warming Arctic, but the effects on the ecosystem could be dramatic.
Flexible foragers of the North
Rockwell had worked with researcher Linda Gormezano on a massive project, training a dog to find bear droppings and wandering more than 300 kilometres of Arctic coastline for three years. Those samples were frozen, transported to the American Museum of Natural History in New York and “painstakingly dissected” by Gormezano, Rockwell says.
Sadly, Gormezano died of an aneurysm, but Rockwell was able to publish her research in papers — and the findings, he says, were groundbreaking.
The massive predators will eat almost anything.
“[Polar bears] come ashore, and they adopt the terrestrial existence,” he says. “And when they have their terrestrial existence, they don’t starve. They simply forage. And the array of stuff that we found that they ate is staggering.”
Geese, ducks, caribou, moose, starfish, ground squirrels, seaweed — “You name it, a polar bear will eat it,” Rockwell says. “Polar bears have ingrained in their genetic blueprint the ability to forage terrestrially.”
This flexibility in diet was a result, Rockwell says, of an animal surviving in the Arctic’s highly variable environment. People might assume the region is simply frozen, but it experiences other seasons — sloppy springs and warmer summers — in addition to its notoriously harsh winters.
In fact, many Northern animals, from wolves to foxes, will eat almost anything available to them, Rockwell says. Foraging for food is an “anything goes” exercise.
“If the only thing you could do is eat seals on the ice,” Rockwell says, “you would have gone extinct.”
‘The bear always loses’
Knowing that polar bears have survived past ice-free periods and feast widely on land every summer does not minimize the impact of climate change, Rockwell points out.
Changes in the feeding habits of these apex predators will ripple through the ecosystem around them. If one bear ate 280 eggs in a few days, imagine what a population of hungry bears that didn’t catch enough seals in winter could do.
Even beyond that, Rockwell is concerned for what may be an inevitable showdown: polar bears, like their black and brown bear cousins, will likely move closer to humans to raid garbage or attack pets, such as dogs.
“That’s increasingly what they’re doing,” he says. “And that’s going to cause a problem because it’s increasing the potential for human-bear conflicts. And tragically, when bears and humans conflict, the bear always loses…. We’re going to lose more polar bears due to gunfire than we are due to starvation.”