The Arctic Omnivore’s Dilemma
As the North heats up polar bears take to dining on land.
Now this is going to make some seals in the Arctic very happy: polar bears are moving off their blubber-rich diets and favoring leaner, land-bound cuisine.
According to researchers from the American Museum of Natural History, polar bears in the Hudson Bay Lowlands have expanded their palates to include snow geese, caribou, berries, grass, and even marsh algae. Such flexibility is astonishing, even for omnivores as versatile as bears. But with the Arctic ice cap melting fast, the polar bears are having difficulty finding solid ice from which they can hunt seals.
So the bears are being forced to hunt and forage off the ice. Trouble is, digging into a flock of little auks isn't quite as filling as chewing on a seal pup. It's like going from a feast of prime rib and mashed potatoes, to a meager helping of chicken and boiled carrots. This cutback in fatty foods coupled with highly taxing activities--running, exploring, climbing cliffs--can lead to depleted stores of energy.
After watching several high-speed chases between polar bears and snow geese, PhD student David Iles and his team from the American Museum of Natural History wondered if these robust mammals, some of which can weigh up to 1,400 pounds, would be able to live off the land. The majority of the successful hunts they witnessed involved geese that were molting and therefore, flightless. But if the fowl only molt in the summer, would the bears be able to make up for energy expended during the other three seasons? Yes, to some extent they can, say American Museum of Natural History biologists Linda Gormezano and Robert Rockwell. After discovering excessive levels of low-energy, high-mineral vegetation in polar bear scat, they concluded that the animals are still able to gain weight on a plant-based diet.
Eggs--primarily those of geese--are also a good source of nutrition. These yolky, ovoid treasures have long been easy pickings for lumbering polar bears (as proven by the video below). A bear will demolish an entire nest for a net worth of 800 to 900 calories. Multiply that by 100 or 200 clutches in and the ravenous bear has consumed 8,000 to 18,000 calories in half a week. In comparison, an adult seal can provide up to 75,000 calories--mostly in fat--and will stave off hunger for more than eight days.
As polar bears further shift from hunting on the ice to feeding on land, the rest of the food web will likely adjust as well. But more research is needed to determine how. A little bit of resilience on the polar bears' part may buy scientists some time to find out.
*The article incorrectly mentioned that the bears from the Hudson Bay Lowlands had added barnacle geese to their diets instead of snow geese. It has also been changed to specify that the video was taken in Svalbard, Norway, in relation to a different study.