Life is hard for the world's largest land carnivore, and getting harder. Even though they're named Ursus maritimus for their swimming ability, a new study has confirmed that without the ice they're in trouble. From the latest Nature:

A census of polar bears in Canada’s Hudson Bay has lent some hard numbers to the long-held fear that retreating sea ice is causing some bears to starve or drown.

Biologists have predicted that polar bears will struggle to survive as summer comes sooner to the Arctic. Less time spent on icy hunting platforms means the bears are slimming down before winter sets in. And there were anecdotal reports in 2005 of more bears found swimming far out at sea; a few were found floating dead, presumably drowned. But so far no evidence has directly linked the trend of melting sea ice associated with climate change to bear deaths.

Now, looking at 20 years of data from bears captured along the coast of Hudson Bay, a team of scientists from the United States and Canada has found that fewer of the youngest and oldest bears survived in years when the ice broke early.

“Survivorship has dropped in the cubs, subadults and very old animals and is directly related to the date of break-up,” says Ian Stirling, a biologist with the Canadian Wildlife Service in Edmonton, Alberta, and an author on the report.