Time of moul­ting of polar foxes con­trol­led by tem­pe­ra­tu­re

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.

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