It is lively outside the foxes' den up in Adventdalen. The parents keep pace as the young ones play, and periodically there's a gap between them as one of them goes out to find food. Around the den are the wings of geese and remains of reindeer calves, which are seen in pictures from a surveillance camera that has been at work during the summer. At 18 fox dens in Adventdalen and Sassendalen there is much activity.
This was not what the researchers expected when they started this year's fox expedition. Record populations of ptarmigan and reindeer indicated at the outset a low mortality rate during the winter. With few carcasses on the tundra, it was expected many fox dens would be empty. Instead, there also ended up being a record fox population in the Adventdalen/Sassendalen area, which is one of the areas where monitoring is going on.
"We have never tallied so many fox litters in the areas we have surveillance. There are also other factors that come into play, but we do not know about those," said Eva Fuglei, a Norwegian Polar Institute researcher who has spent nearly four weeks in the field with Stefan Prost and Dominique Berteaux. Meanwhile, Bjørn Anders Nymoen and Finn Slette are accounting for the observations at Brøggerhalvøya.
Fuglei, who has followed the fox population for many years and has led the work with the field teams, admits they were both surprised and do not know the reason why the number of dens with pups has increased this year.
"That's what makes this so exciting," Fuglei said. "We put together pieces to understand the whole picture and we have found that is important for youngsters to have a supply of reindeer carcasses. Therefore, I imagined that there would not be more foxes this year."
Reindeer counts made earlier this summer show there has never been as many reindeer in the areas since the counts began in 1979 Few deer carcasses were observed in the areas during the count, suggesting a low mortality rate, while at the same time many calves and yearlings were seen.
The arctic fox is one of ten "flagship species" selected by the International Union for Conservation of Nature and Natural Resources (IUCN) to illustrate the effects of climate change. While the species is on the Red List as endangered on the mainland, the Svalbard population is considered sustainable.
It is likely today's population is the consequence of a mild winter that required less energy consumption and a supply of food that has been very good.
"The rapidly increasing geese populations that come to Svalbard to breed are an important food source for foxes," Fuglei said. "The geese arrive in Svalbard in early May before the puppies are born. We find goose wings at the dens, so we know that the foxes take adult geese. The large number of reindeer calves born in June is another food source that may affect breeding success. This summer we have seen a significant increase in the remaining amount of calves at the fox dens."
"This is quite new with all these calves," she said. "I have not seen so many before and it is probably due to the fact that there have been many females who have had calves. And the foxes are opportunists."
The ice melts
The researchers are now also speculating that less sea ice may make life easier for the foxes because seals are losing good hiding places where they can give birth. Typically, this occurs in the snow caves out on the sea ice, but the ice-free fjords and less snow makes it easier to locate seal pups.
"One factor we do not currently have such a good insight into is how the food supply from the marine system affects fox breeding," Fuglei said. "Our long monitoring series will be important to understanding what affects arctic fox breeding and how climate change is affecting ecosystems in Svalbard."
Fox territories vary in size depending on the availability of food, ranging from eight to ten square kilometers down to three or four if the den is 'the dinner plate.' The critical time for the young foxes is from October when they must leave the den and manage for themselves.
"It will be very interesting to see how it goes this winter," Fuglei said.