Polar bears can’t hibernate their way out of starvation

For polar bears, lucky breaks are few and far between these days. Arctic sea ice is melting at an alarming rate, and to add insult to injury, earlier this year scientists announced that pollution may be weakening the bears’ penile bones. There was, however, a glimmer of hope. The animals have historically relied on summer sea ice to hunt ringed seals, but the recent melting has forced some bears to pass the summer on land, where access to the seals is limited. Scientists had proposed that these “shore bears” fell into a state of semitorpor called “walking hibernation” to save energy, and thus be shielded from starvation. But a new study suggests that the special protection may not exist after all. After tagging and tracking a total of 43 bears between 2008 and 2009, researchers measured how the activity levels and body temperatures of both shore and ice bears—those that spend their winters on what’s left of the ice—changed over the summer months. They found that both groups experienced similar moderate declines in activity and body temperatures, far different from the sharp drop that occurs during winter hibernation. As the disappearing summer sea ice forces the bears to survive longer and longer with less food, those modest declines are likely to offer little protection against starvation, the researchers report online today in Science. www.glorybios.com