As regular Foxtrail readers will know, Fjällräven has been supporting the research into the Scandinavian arctic fox population since the 1990s, a period of time that saw numbers plummet and the species became critically endangered. Part of our support has included the financing of a PhD position at Stockholm University, and for the past four years or so, that position has been held by Rasmus Erlandsson. We caught up with him earlier this year for a more in depth look at the differences between the varying lives of arctic foxes around the arctic region.

Image: Even Agerup

Arctic foxes aren’t just white red foxes living in the Arctic. They are a species all of their own. But within the species, local climate and ecological situations mean regional differences occur. “Biologists commonly divide arctic foxes into two different ecotypes,” explains Rasmus. “They all belong to the same species, but arctic foxes that rely on food from the sea – the coastal ecotype – live very different lives to those that mainly eat small rodents – the lemming ecotype.”

The resulting differences usually manifest in the size/weight of the foxes and also the size and frequency of their litters. Coastal foxes give birth to around four to seven cubs per year. Lemming foxes, on the other hand, have litters ranging from one to eighteen, and some years, when food is scarce, they decide not to breed at all.

Basically, it’s food that determines the survival and success – or lack thereof – of arctic foxes around the Arctic. It’s not that they’re fussy eaters, “they eat almost anything they can get hold of,” says Rasmus. It’s more that their food sources – rodents, birds, eggs – are linked to larger, external factors, notably climate change and fluctuations in sea ice and the lives of local predators. “While many of the arctic fox populations in the world are doing just fine,” says Rasmus, “others are threatened by extinction”.

Let’s take a closer look at the North American arctic fox. The population there is estimated to be around 110,000 mainly in Canada and Alaska. Most arctic foxes in this region are lemming fox ecotypes, as they live in areas with at least one small rodent species, notably lemmings. However, lemmings are unpredictable, to put it mildly. Sometimes they are in their millions, swarming over the landscape. Other years not a single soul is to be seen. This is problematic for arctic foxes and all other animals that rely on lemmings for food. North American arctic foxes start looking further afield. In the summer, when up to one million geese make home on the tundra, brave arctic foxes steal their eggs and store some of them away for leaner winter times. But sometimes even this isn’t enough. In this case, arctic foxes, weighing roughly 3.5kgs, start tracking polar bears, weighing roughly 150-450kgs. Talk about punching above your weight. It’s not that these big bravado arctic foxes take on the polar bears directly. They actually eat the leftovers from seal carcasses, once polar bears have finished gorging themselves.

 

“However, we have actually seen that arctic foxes are able to locate the bird lairs of ringed seals through smell. Once they find one, they through the snow dome and kill the unprotected seal pup. Since a large seal pup can provide enough energy to keep a fox alive for almost a year, it’s no surprise the seals provide an important food source,” says Rasmus.

Because of these options and their bravery and cunning,

the North American arctic fox is doing quite well. However, shrinking sea ice and milder climates can have a major negative impact in the future.

Icelandic arctic foxes have not had sea ice since the last ice age, so what do they do about food? “Iceland hasn’t been connected to sea ice for a long time, so no foxes can more in or out of the island. We normally see populations on isolated islands show special characteristics, as local conditions favour certain traits. But it’s not only genetic isolation that’s special in the Icelandic case; they live in a quite different ecological setting for an arctic fox,” says Rasmus.

The Icelandic arctic fox, unlike those in North America, is a coastal fox ecotype. This is because there’s an absence of cyclic small rodent species on Iceland. But there’s also a lack of natural predator, too. Despite its small size, Iceland is actually quite varied – or at least for arctic foxes.

“The beaches in the western parts of the country have a lot more birdlife and other food resources than those in the east,” says Rasmus. “Inland the accessibility to marine food and sea birds is, of course, limited or non-existent. In the eastern parts, however, there are wild reindeer, and in large parts of the country domestic sheep roam freely. This means that even though the Icelandic arctic foxes belong to the coastal ecotype, life is pretty different if you live inland or along the coast. And if you live along the eastern coasts with less food, or the more productive western ones.”

So what do Icelandic foxes do about this? They mostly eat insects and berries. They seem to be a lot lazier than their North American counterparts if you ask us!)

“Well those living close to the sea do eat sea birds, ducks, geese and seal carrion. And inland foxes also eat birds, but the Icelandic foxes sniff out whatever food is available. And when there’s not enough of the good stuff, the foxes eat the larvae and pupas of the kelp fly that live in decomposing seaweed or start to pick berries. Perhaps some are just lousy bird hunters,” jokes Rasmus.

Basically, it means they are flexible. But evidence shows that Icelandic arctic foxes can’t regulate their litter depending on food availability. However, more food available means less conflict over territory, explains Rasmus, and this means more litters overall.

Like in North America, numbers of Arctic foxes in Iceland are healthy, so much so that government sponsored culling killed between 4,000 and 5,000 foxes in 2000. But that’s not to say a warmer future won’t pose problems. Problems that Scandinavian arctic foxes have already been facing.

Image: Klara Jansson

Scandinavian arctic foxes are lemming foxes in a true sense: “almost all aspects of their lives can only be understood with a lemming perspective in mind,” says Rasmus. Lemmings’ breeding cycles usually work on a four-year frequency in a pattern of boom and bust.

“If we presume a four-year lemming cycle, it will mean the foxes have rather large litters two years in a row. Firstly when the small rodents are increasing in numbers and then during a peak. Cubs that are born during the increase year will have a good chance of surviving and then be able to breed the following year. Thus when an increase year is followed by a peak year, litters are not only big but the number of breeding foxes will also be big, as many of the young foxes survived. The effect of two good years following each other is therefore much bigger than two separate good years,” explains Rasmus.

But what happens if the lemmings skip a year, which they’ve been known to do? This is what happened in Scandinavia during the 1990s. The lemmings simple disappeared. And this was devastating for the arctic fox. But their fate was actually sealed much earlier when they were hunted almost to extinction in the first part of the 20th century because of their beautiful fur.

Add to this localised in-breeding and the encroachment of the red fox and you have a disastrous situation for the arctic fox. In-breeding meant lower resistance to scabies, which was brought in by the red fox, which also competed with the arctic fox for food and territory. The red foxes were moving into the arctic foxes’ territory because of climatic changes, i.e. a warming climate and a spread of boreal forests.

Thankfully conservationists and scientists stepped in. Through captive breeding and release, feeding and giving medicine to arctic foxes numbers in Scandinavia are starting to increase. “We don’t know for sure whether the future looks bright for Scandinavian arctic foxes, but the steady increase in the number of foxes since the 90s is encouraging and a sign that the conservation measures, that were initiated based on the research from the Swedish arctic fox project, do help,” says Rasmus.

But lemmings continue to breed in erratic cycles, red foxes continue to move in and climate change isn’t going away – far from it! And although the life and times of the arctic fox varies greatly around the arctic, one thing is for sure: nothing is certain.

“My research,” says Rasmus, “aims to understand how the landscape affects the arctic foxes: why foxes in some areas are more successful than others? With increased understanding of the different factors that affect the ecosystem and thereby the arctic foxes, we can improve the conservation measures, and hopefully the Scandinavian arctic fox population will become so big that it is able to manage on its own in the future. Just like the North American and Icelandic populations are doing now.”

 

Text: Sarah Benton & Rasmus Erlandsson