Polar foxes (also known as “arctic fox”) moult twice a year, with a change from the thicker winter fur to the thinner summer fur in spring and back again in autumn. Both kinds of polar foxes do that: the white fox with the prominent change from white winter fur to brown summer fur and back, and the blue fox which is – no, not blue, but brown throughout the year.
Next to thermal isolation, camouflage can be an important function of the fur, at least for the white fox, and this requires a synchronised timing of the moulting and the snow melting/fresh snow periods.
Polar fox, fur version 1: Blue fox.
So far, scientists assumed that the timing of the moulting period is largely controlled by the length of daylight. This could be problematic if the timing of the snow melt/fresh snow period gets decoupled from certain customary daylight length values. This might result in animals still having white winter fur on brown tundra when the snow melt is through, earlier than in previous times, and this again would involve a loss of camouflage: the animal has a higher risk of falling victim to a predator or possibly to reduced hunting success if it itself is a predator, such as the polar fox.
Polar fox, fur version 2: white fox in summer coat.
But recent scientific data indicate that the timing of the fur change may be coupled to temperature and snow cover development rather than to the length of daylight, as biologist Lucie Laporte-Devylder and co-authors from NINA (Norwegian institute for nature research) write in a scientific publication Laporte-Devylder used photos taken over years by automatic cameras and correlated them with meteorological and snow cover data. The result indicates that temperature and snow cover are a significant factor for the timing of the fur change of polar foxes. This might mean that polar foxes are better able to adjust to climate-change-induced changes the snow cover then previously believed.
Polar fox, fur version 3: white fox in winter coat.
The data are from the Snøhetta area on the Norwegian mainland. The results may, however, not be fully applicable to the polar fox population in Svalbard. On the mainland, polar foxes with bad camouflage run a higher risk of predation by sea eagles, but there are no eagles or other large birds of prey in Svalbard.
There, however, polar foxes have an entirely different problem with their fur: lice are currently becoming more and more common in Svalbard. So far, nobody can tell where they are coming from and what the consequences will be for the affected foxes.