In ten years biologist Didrik Vanhoenacker has only seen similar squirrels a few times.
Therese Norberg snapped the photo of the squirrel on New Year's Eve at her mother’s place in Norsjö. It is not unusual for squirrels to turn up in the area but neither Therese nor her mother have previously seen one with a white tail.
– During this winter my mother has caught a glimpse of this squirrel several times. She has mentioned it on several occasions and now I also got the opportunity to take a photo of it, Therese says.
– It is really awesome that it has a white tail. That means that you recognise it every time you see it, as opposed to other squirrels.
Therese is reacting to the fact that the tail is bright white while the rest of the squirrel looks like a regular squirrel.
– I thought that it perhaps has had an injury, that the tail has grown out again or something like that, she says.
We get in touch with Didrik Vanhoenacker, who is a biologist at the Swedish Museum of Natural History. He confirms that two-tone squirrels like the one Therese saw in Norsjö are unusual.
– I have seen this just a few times over ten years. Perhaps five or six times in total. It is absolutely unusual, he says.
Despite what you might think its not a matter of albinism, says Didrik Vanhoenacker. In that case the entire squirrel would be white with red eyes.
– This is rather some sort of pigmentation defect on a certain section of the fur. The pigmentation is not coded into the fur and the squirrel ends up with white sections.
– This is fairly common for some birds. Blackbirds for example can have some white spots.
The defect must have occurred when the squirrel mother was pregnant and the foetus only was a couple of lumps of cells, he explains.
– All cells that originate from the defected cell will then lack the ability to store pigment. That means that the whole tail has the same defect. Had the same thing happened in another ”lump of primeval cells”, another part of the squirrel had become white, says Didrik Vanhoenacker.
This is also a great disadvantage to the squirrel who will become more visible to predators such as goshawk or marten.
– This squirrel probably has worse chances of survival than a squirrel with normal pigmentation. It is much easier to discover. Which is a shame because it is very pretty, says Didrik Vanhoenacker.