Ermine Puzzle

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image josef hlasek –

Driving out to dinner on Wednesday night, a beautiful stoat soared across the road in the car headlights. She was gone in a heartbeat, but I’d seen enough to mark brown forelegs and a brown head, then a brilliant white cape to the bristling tip of a black tail. I’ve seen less than a dozen white stoats in my life, and this glimpse was cherished beside a handful of other sparkling encounters.

But it set me to thinking. Not every stoat turns white in the winter, and I’ve seen brown stoats in every month of the year. If some stoats turn white and others don’t, there must be some genetic coding which dictates change for a proportion of the wider population. I’ve never seen a stoat that was 100% white, and so I start to wonder why.

It takes time to change your coat’s colour, and so maybe white stoats are only pure white for a few weeks each year. They’re probably somewhere in between brown and white for the rest of the winter, and perhaps this explains why even the whitest stoat always seem to have some brown about them. My absurdly detailed notes record that I trapped a white stoat on the 5th March 2011. This was the whitest stoat I’ve ever seen, but being able to study the beast at close hand, I found that it had brown spectacles around its eyes. It was only 95% pure.

Perhaps a move towards warmer, milder winters will begin to select against winter whiteness, but then I wonder if maybe there’s a middle ground between brown stoats and white ones. Maybe some only turn half white and consider the job done. Maybe that’s how the pure white colouring will gradually fading away in a warmer world. I suppose the only way to tell for sure would be to follow the progress of a single stoat all winter, but anyone who knows about wild stoats would see that’s a non-starter. They move so quickly and with such dazzling excitement that you might as well track the progress of a spark.

It’d be interesting to hear if any readers have pondered this, because while stoats are ineffably cool and interesting animals, it’s not easy to find any good information on their ecology and the science of that colour change.

One thought on “Ermine Puzzle

  1. Jonathan Pointer

    My wife and I were suprised to see a white stoat running through a roadside larch plantation on a winter some 15 years ago. The location was the South Downs on an un remarkable southern winter that was marked by a few frosts and no snow. I seem to recal somewhere that trials have been done on Stoats where they were put into a large industrial freezer and subjected to various levels of cold until the “trigger” that clicks them white happens-might be worth researching..

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