Polar bears on Svalbard tend to leave dens earlier

Polar bear mothers on Svalbard have, in recent years, come out of their winter dens with cubs about one week sooner on average than before 2016. A study by Canadian and Norwegian scientists found this, and the researchers say the shift may be connected to climate change. The study tracks 13 mothers with cubs recorded on Svalbard over time.

Pregnant females normally enter a den in late autumn and stay through the winter without eating. The cubs are born in January or February and weigh around 600 grams, and the den shelters them until spring. The researchers link the earlier departures to the Arctic losing sea ice as temperatures climb. Dr Louise Archer, who took part and works at the University of Toronto Scarborough, gave a figure of about 23% per decade for summer sea ice area lost in the Barents Sea, counted from the late 1970s and 1980s.

Bears depend on ice for hunting, so less ice may mean mothers get fewer nutrients. Archer told the Barents Observer that a female entering the den in poor condition might not manage to stay long enough to support her cubs. The team wants to examine this over a longer period.

Archer has worked on the study for three years. Since 2016, the researchers have travelled to Svalbard for a few weeks to watch when mothers leave their dens. They place video cameras outside the dens, and collars on the mothers send satellite data on body temperature and location.

Archer said Svalbard has around 300 so-called local bears, meaning those that live in the archipelago all year. She said their number has not changed so far. The change is in where they den. The bulk of denning across the European Arctic probably occurs at Franz Josef Land, on the Russian side of the northern Barents Sea. Hopen Island on Svalbard used to be an important denning area, but in recent years the ice has come back late or not at all, so bears cannot cross it to reach such places. Her team is still analysing the data collected this year.