Super Smellers: Polar Bears

Andrew Derocher from the University of Alberta presents the case for polar bears...

If there are champions among mammals with excellent senses of smell, polar bears are on the podium. The bears rely on their sense of smell as they hunt across huge areas of snow covered ice. The short hunting season is a compelling force: what happens during the spring hunt may determine life or death, reproducing or not.

The main prey of polar bears are ringed seals which are hugely abundant and less than keen to be eaten. At their most vulnerable to predation in the spring when giving birth to pups and mating, ringed seals make dens under the snow that piles up on top of jagged ice. These dens have an underwater escape route through the ice.

The key to being a successful polar bear is locating these seal dens. To do so, the bears rely on their sense of smell – all seals have fishy smell and during the breeding season, males have an odour reminiscent of sport socks and petrol. Such a stink might be easy to find out in the open but once under a meter of snow, polar bears have to pinpoint the precise location of the seal.

How far away can a polar bear smell a seal? Lacking controlled experiments, we don’t have great insights but given that there can be hundreds or thousands of seals within a day’s walk, the bears really need their sense of smell to provide their seal’s exact location.

Tracking bears over the sea ice, it’s clear the bears use wind to their advantage: walking crosswind provides a smorgasbord of seal smells but some are obviously more enticing and provoke a sudden upwind stalk. Walking on sea ice is like walking on a drum: one false crunch in the snow and your dinner will escape. The bears use their sense of smell to get close and then use snow structure (possibly even sounds made by the seals) to make their final pounce. If the bear has done its job, it’s a seal dinner.