A new study from the University of Alberta proves that polar bears hunt by their sense of smell while travelling cross-wind, the first evidence of such behaviour in a land-based carnivore. Yet, the bears’ hunting habits may ultimately prove to be a problem, say the researchers, as climate change is expected to speed up wind patterns in the Arctic and make scent-based hunting more of a challenge.
For polar bears, their most sought-after foods are the ringed seal and bearded seal, both of which are hunted out on sea ice. The bears use both an ambush technique (grabbing a seal as it comes up for air at a breathing hole in the ice) and a roaming, active search for seal pupping lairs. The latter approach involves scent more than sight, it turns out, as the seal dens underneath the snow can be hard to spot, even for a hungry bear.
But the specific method used by polar bears has been a mystery up until now, as a new study from researchers at the University of Alberta have concluded that polar bears do their hunting by travelling cross-wind to detect seal scents carried across the sea ice landscape. The theory goes that travelling perpendicular to the wind direction can bring a wider range of smells to the animal, crucial, as seal densities can measure less than one seal per square kilometre, meaning that the bears must travel a lot of ground to find their prey.
“If it’s moving crosswind, it’s constantly encountering new streams of air and constantly learning more and more about what’s upwind of it,” says Ron Togunov of the Department of Biological Sciences at the University of Alberta and lead author of the study, in a statement. “This crosswind movement has been suspected and has only been observed in insects and, more recently, in birds but never for mammals.”
To track the movements of the polar bears, researchers captured 123 adult female polar bears over the course of a ten-year period between 2004 and 2014 and fitted them with GPS-enabled collars (males, it turns out, can’t be fitted with collars because their necks are actually wider than their heads!) The researchers linked up the data on the bears’ movements to surface wind speeds and directions modelled for the bear’s habitat region.
The results showed that during the winter, when wind speeds were lower, the bears most often travelled cross-wind to hunt, while during times of high wind speeds, movement was mostly downwind. The researchers surmise that the higher wind speeds in winter make it difficult for the bears to gauge scents and further cause them to face downwind to avoid the worst of the cold air blast, while the lower wind speed days would be more opportune for scent collection and hunting.
But the fact that the bears need wind speeds to be relatively light to do their hunting is both intriguing and worrisome, says Togunov. Climate change models are predicting changing to weather patterns worldwide, including a picking up of wind speeds in the Arctic, a situation that could spell trouble for the polar bears’ scent-based hunting.
“Faster wind speeds might decrease the hunting success,” says Togunov. “It raises more questions.”
The new research is published in the journal Scientific Reports.