A stoat and its Lordly winter coat
On 25th February 2020 Pam Mackenzie sent me two pictures of a stoat in her garden at Achnacarnin (NC0431). It was in the winter coat known as ermine, almost pure white except for a little brown on its head and the black tip to its tail, which never changes colour (photos 1-2). She has seen it several times since that day and informs me that their ‘local’ stoats always change into ermine for the winter.
Later, Pam informed me that Karen Morrison had posted on her Facebook page more pictures of a stoat, taken on her smart phone on 29th February. It had appeared on the decking of a ‘pod’ half way up the back road at Culkein Stoer (NC0333). Karen kindly sent the pictures on to me (photos 3-4). This stoat shows no sign of a white winter coat (other than the belly, which always remains white).
Stoats are not uncommon in the coastal parts of Assynt, and along the limestone corridor between Inchnadamph and Elphin, all areas that have, or had, thriving rabbit populations. They are regularly reported in ermine in the winter, perhaps not so surprising in the north of Scotland.
However, the difference in coat colour of the two recent sightings prompted me to consult the definitive account of the species in the Handbook Mammals of the British Isles (4th edition, Harris and Yalden, 2008). From this I learned that the moult into a thicker, warmer, winter coat, takes place in October and November. It is triggered by reducing day-length, and occurs long before there are any indications of how cold the coming winter may be, and how long snow may lie.
A white coat will protect a stoat from possible predators, such as foxes or birds of prey, in a snowy landscape, but otherwise renders it much more conspicuous. The black tip to the tail may deflect the strike of such predators. Females are more ready to adopt a white coat than males, but how do any of them ‘decide’ how far to go? And what might be the effects of climate change on the incidence of this phenomenon?
The title relates, incidentally, to the use of stoat skins in the past to trim the regalia of the nobility and judiciary.