1.

The Arctic fox is the terrestrial mammal species with the widest distribution in the Arctic. This is due both to the fox’s exceptional ability to live in some of the most hostile environments on Earth and to its capacity for long-distance movements. The extraordinary mobility of the Arctic fox was noted by the Norwegian polar hero Fridtjof Nansen in 1885, when he found fox tracks close to the North Pole. In modern times, telemetry has made it possible to record in detail how individual foxes move and use habitat within their normal home ranges, as well as when they wander to find new homes. In a project financed since 2012 by Fram Centre’s Climate-ecological Observatory for Arctic Tundra (COAT) and the ICE program of the Norwegian Polar Institute, we have equipped more than 60 Arctic foxes on Spitsbergen with satellite collars to study their spatial ecology. We are particularly interested in how they use land and sea ice in Svalbard, which is changing rapidly due to climate warming. While several of the foxes we have been monitoring ventured onto the sea ice, only one ended up outside Svalbard.

Place of origin

The Arctic fox in question was captured 29 July 2017 near the terminus of the glacier Fjortende Julibreen in Krossfjorden, Western Spitsbergen. It was a young female, born the same summer probably in the same area and she was of the blue colour morph. Arctic foxes come in two colours types (morphs), blue and white. The blue colour occurs most frequently in coastal areas without sea ice, such as in Iceland. In Svalbard, blue foxes make up approximately 7% of the population. Before the fox was released, she was outfitted with a satellite collar that made it possible for us to track her position every day. Little did we know she would undertake an epic journey, providing us with detailed evidence about how such long-ranging dispersal occurs.

The Arctic fox stayed put for seven months. In early March 2018 she started to explore northern Spitsbergen, moving across land and along ice-free shores until she met with sea ice for the first time on 26 March 2018.

Traveling on sea-ice

After stepping out onto the sea ice she headed north and later west towards northern Greenland. While on the sea ice she moved with an average speed of approximately 46 km/day. On two occasions, she had short stopovers (7-8 April and 10-11 April), which may indicate that she had encountered physical barriers on the sea ice or bad weather – or food. The pack-ice north of Svalbard is a dynamic environment characterised by frequent formation of leads: stretches of open water which appear in the ice, then close again. Leads can be biological hot spots for amphipods, seabirds and marine mammals, and may thus have offered the traveling fox a much-needed meal. Conversely, leads can be obstacles – cracks several hundred metres wide, opening and refreezing over the course of a few days. Blizzards or other adverse weather conditions may also have forced the fox to find shelter until conditions improved.

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To a Canadian area named by Norwegians

After having crossed the northern tip of Greenland, the Arctic fox returned to the sea ice again at Kane Basin on 6 June 2018. Four days later she set foot on Ellesmere Island, Nunavut, Canada, 76 days and 3512 km after leaving Spitsbergen. The fox continued westward to the Fosheim Peninsula, which she reached on 1 July 2018. This peninsula was named by the Norwegian Polar explorer Otto Sverdrup, leader of the second Fram expedition in 1898-1902. In 1899 they explored this area and named the peninsula after Ivar Fosheim, a Norwegian from Vestre Slidre in Valdres, who joined the expedition as a jack-of-all-trades. The Arctic fox stayed on Fosheim Peninsula until the satellite collar stopped transmitting on 6 February 2019, six months later.

Natal dispersal in arctic globetrotters

It is quite normal that young animals move away from where they were born to settle in a new area where they may stay for the rest of their lives. This strategy, termed natal dispersal, is a way to find a territory that provides better possibilities for a successful life. Natal dispersal can be either a fixed, innate behaviour to avoid inbreeding, or conditionally induced by local competition for food, mates, or den sites.

Which of these potential drivers of natal dispersal caused the young blue female to leave Spitsbergen is unknown. What is certain, however, is that it gave us a unique insight into how far and how fast such dispersal can be in Arctic foxes, and highlighted how important polar sea ice is in connecting the continents for these Arctic globetrotters.