As summer and autumn sea ice diminishes in the Arctic Sea, polar bears spending more time on shore have been spotted eating eggs, hunting down the nesting birds that lay them, hunting other land animals and even chewing on edible plants growing onshore.
But is that enough to sustain them in an ice-scarce Arctic?
No, says a new study by scientists from the U.S. Geological Survey, Washington State University and Polar Bears International.
The study analyzes food needs of polar bears, including their genetic metabolic characteristics, and the characteristics of the onshore ecosystems and the foods in them.
The verdict? Terrestrial foods are, for the most part, the wrong kind for fat-dependent polar bears, and there is too little of it. What bear food does exist on land is already being used by Arctic grizzly bears, which -- appropriately -- are the smallest and most spread out of all the world’s brown bears, said the study’s lead author, USGS research biologist Karyn Rode.
The study, published Wednesday in the journal Frontiers of Ecology and the Environment, find that even though polar bears are spending more time ashore and are affecting terrestrial ecosystems, “evidence suggests that the nutritional contribution of terrestrial foods to polar bear diets will probably remain negligible.”
As the world’s biggest bears, and as denizens of the cold Arctic climate, polar bears need large amounts of fat in their diet to survive, said co-author Steve Amstrup, a former Alaska-based USGS biologist who is now chief scientist at Polar Bears International.
“All bears are not created equal, and if you’re a really big bear, like a polar bear, you need to have a rich food source to sustain you,” Amstrup said.
Ringed seals, the primary prey for polar bears, are precisely that rich food source, with fat accounting for up to half their body weight, Amstrup said. The food sources on land cannot compare in quality or quantity, he said.
Consumption of bird eggs, birds, shore plants and even seaweed is not necessarily widespread, Rode and Amstrup said. Only a small portion of any of the world’s polar bear populations have been observed doing such foraging, Rode said. And an important indicator that it is not doing much to help overall polar bear survival is that in the places where such behavior has been most frequently documented, polar bears have declined in population and in body condition, she said.
In some cases, polar bears have gone to extraordinary lengths to get at their alternate food sources. The study includes a photograph from Svalbard showing a bear perched precariously on a ledge in Svalbard and trying to get at murre nests lodged in the steep rocky cliff there.
But is that enough to sustain them in an ice-scarce Arctic?
No, says a new study by scientists from the U.S. Geological Survey, Washington State University and Polar Bears International.
The study analyzes food needs of polar bears, including their genetic metabolic characteristics, and the characteristics of the onshore ecosystems and the foods in them.The verdict? Terrestrial foods are, for the most part, the wrong kind for fat-dependent polar bears, and there is too little of it. What bear food does exist on land is already being used by Arctic grizzly bears, which -- appropriately -- are the smallest and most spread out of all the world’s brown bears, said the study’s lead author, USGS research biologist Karyn Rode.
The study, published Wednesday in the journal Frontiers of Ecology and the Environment, find that even though polar bears are spending more time ashore and are affecting terrestrial ecosystems, “evidence suggests that the nutritional contribution of terrestrial foods to polar bear diets will probably remain negligible.”
As the world’s biggest bears, and as denizens of the cold Arctic climate, polar bears need large amounts of fat in their diet to survive, said co-author Steve Amstrup, a former Alaska-based USGS biologist who is now chief scientist at Polar Bears International.
“All bears are not created equal, and if you’re a really big bear, like a polar bear, you need to have a rich food source to sustain you,” Amstrup said.
Ringed seals, the primary prey for polar bears, are precisely that rich food source, with fat accounting for up to half their body weight, Amstrup said. The food sources on land cannot compare in quality or quantity, he said.
Consumption of bird eggs, birds, shore plants and even seaweed is not necessarily widespread, Rode and Amstrup said. Only a small portion of any of the world’s polar bear populations have been observed doing such foraging, Rode said. And an important indicator that it is not doing much to help overall polar bear survival is that in the places where such behavior has been most frequently documented, polar bears have declined in population and in body condition, she said.
In some cases, polar bears have gone to extraordinary lengths to get at their alternate food sources. The study includes a photograph from Svalbard showing a bear perched precariously on a ledge in Svalbard and trying to get at murre nests lodged in the steep rocky cliff there.
That might be a sign of desperation, Amstrup said. “Foraging on the high cliff is very, very high-risk and the bears have to be really hungry before they take on that risk,” he said.
by Yereth Rosen, Alaska Dispatch | Read more:
Image: Loren Holmes
