How to catch a polar bear

From a helicopter, it can be hard to spot a polar bear against the frozen tundra. So when the polar bear biologist Jon Aars heads out for his annual research trips, he scans the landscape for flashes of movement or subtle variations in color — the slightly yellowish hue of the bears’ fur set off against the white snow.
“Also, very often, you see the footprints before you see the bear,” Dr. Aars said. “And the bear is usually where the footprints stop.”
Over the decades, research trips have shed light on the basic biology and ecology of the bears and, in recent years, helped scientists keep tabs on how the animals are coping with climate change. The rapid habitat changes are already affecting their behavior; with the sea ice retreating quickly, some of the bears now have to swim long distances in order to find places to den. But so far, the bears themselves still seem robust, Dr. Aars said.