Rising temperatures are forcing polar bears to shift their migration patterns. The bears are opting for new routes because of changing sea ice.

A new study focuses on the migration patterns of polar bears in Hudson Bay, Canada and used satellite-tracking data from between 1991 and 1997 and 2004 and 2009. The researchers were able to predict when the bears migrated on and off the ice based on how quickly the sea ice melts and its distribution in the bay. The study was published Tuesday in the Journal of Animal Ecology.

"Keeping track of when polar bears move on and off the ice is an important aspect of monitoring the risks to the population associated with climate change," Seth Cherry told Live Science. Cherry is a graduate student in ecology at the University of Alberta, Canada and the leader of the study.

Walking out onto sea ice is incredibly important for polar bears. The bears' main food source is seal, and they do most of their seal-hunting out on the ice. When they are forced to spend more time on land, they must rely on fat reserves while they wait to get back onto the sea ice.

"Climate-induced changes that cause sea ice to melt earlier, form later, or both, likely affect the overall health of polar bears in the area," Cherry said.

The team tracked 109 female polar bears using tracking collars equipped with GPS transmitters that broadcast the bears' locations. The researchers also measured the bears' diet and nutrition using blood samples and fat biopsies.

"When we look at the migration patterns of the collared bears, it appears as though bears in recent years are arriving on shore earlier in the summer and leaving later in the autumn," Cherry said. "These are precisely the kind of changes one would expect to see as a result of a warming climate."