Where do arctic foxes go in winter?

Submitted by editor on 25 November 2016.Get the paper!

Tracking wild carnivores is never easy. They are fast, elusive, often nocturnal, and rarely abundant. This task can be even more daunting when a species is too small to wear a tracking device that is remotely heavy or if individuals have the ability to travel very long distances (over thousands of kilometers). Add to this a period of 24-hour darkness, temperatures often falling below -40°C and extreme weather conditions, and you have the arctic fox study system in winter.

On Bylot Island (Nunavut, Canada), all known arctic fox dens in the 600-km2 study area are visited in mid-May to monitor fox activity. The sky is already constantly lit by the midnight sun, but temperatures are still around -10°C. Photo: Sandra Lai

As an important furbearer, the arctic fox has been studied for several decades. However, the harsh conditions in the Arctic have prevented the intensive study of many aspects of its winter ecology. In regions where sea ice is present during winter such as in Russia, Alaska and Canada, observations of individuals on the sea ice have earned the arctic fox the nickname “northern nomad” or “ice traveller”. Since the 1940s, several papers have sporadically related seasonal migrations of arctic foxes from the tundra to the sea ice. After spending the winter on the sea ice, possibly feeding on polar bears’ seal remains, homing foxes are believed to return the tundra to breed and raise their young during summer. As a small rodent specialist, many aspects of its ecology are linked to the cyclic dynamics of its prey. Mass emigrations of foxes, possibly related to the decline in the lemming populations, have been described in Russia and the Canadian province of Manitoba. As seen in avian predators specializing on cyclic rodent populations, the long-distance tracking of the rodent resource has also been suggested for arctic foxes. Resident populations exist however, for example, in Iceland (which is surrounded by open water all year round) or in the Scandinavian alpine tundra. So, where do arctic foxes go during winter?

A female arctic fox wearing an Argos satellite collar. Photo: Josée-Anne Otis

Thankfully, the miniaturization of batteries and transmitters now allows us to use Argos satellite collars on the small-sized arctic fox. Equipped with very lightweight and long lasting batteries, these collars let the animals’ locations be sent via satellites. Therefore, individuals need not be recaptured for us to retrieve data from the devices (which is essential when an animal may end up hundreds of kilometers away from where it was initially caught).

In our study area on Bylot Island, which is one of northernmost sites (73°N) where arctic foxes are studied in the world, we were able to obtain for the first time movement tracks that covered their entire annual cycle (from one breeding season to the next). It allowed us to record complete winter tracks and determine whether long-distance movements corresponded to breeding dispersal or migratory movements.

The Bylot Island Research Station conducts a long-term monitoring of all animal populations, vegetation and climate of the arctic tundra. Photo: Sandra Lai

Not only did we track a very mobile species using a new technology, but we also worked closely with other research teams on Bylot Island. The long-term monitoring of the entire ecosystem that is performed on the island (http://www.cen.ulaval.ca/bylot/index.html) provided important data on the arctic fox’s terrestrial prey species, lemmings and snow geese (mostly eggs). This allowed us to link movement patterns to resource dynamics.

Much to our surprise, our initial assumptions that this fox population switches to a migratory pattern or emigrates massively during winters of low lemming densities were not confirmed. On the contrary, the majority of foxes remained resident over the winter, opting to do short-term commuting trips to the neighboring sea ice when terrestrial resources were scarce. While discussing preliminary results, Dr. Erik D. Doerr (Australian National University) told me that “it’s amazing how often people's assumptions about animal movements turn out to be completely wrong once someone actually does some tracking”. Nevertheless, as shown in our recent paper published in Oikos, not all of our assumptions about movements were incorrect. Moreover, our results also do not discredit the existence of mainly nomadic or migratory arctic fox populations. Finding these populations may help further understand which factors shape movement strategies and what ultimately determines a resident, nomadic or migratory lifestyle.

The authors through Sandra Lai

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