SEA­SONAL COLOUR CHANGE

BBC Wildlife Magazine - - Wildlife Essay -

Most mam­mals in tem­per­ate cli­mates dis­play win­ter adap­ta­tions of one kind or an­other, such as weight gain, food hoard­ing, mi­gra­tion, hi­ber­na­tion or tor­por. Sea­sonal moult­ing is usu­ally trig­gered by the length of daylight hours, known as pho­tope­riod. This is the most ac­cu­rate means by which an or­gan­ism can per­ceive sea­sonal change, be­cause tem­per­a­ture and other weather con­di­tions are much more vari­able. The trans­for­ma­tion isn’t nec­es­sar­ily com­plete – for ex­am­ple, snow leop­ards moult from buff-coloured to white but keep their spots, while stoats adopt a coat of pure white ex­cept for their tail-tip.

Moun­tain hares may re­tain a vari­able amount of buff or brown (es­pe­cially on the head), while the tips of their ears also re­main black.

Clock­wise from top right: stoat, moun­tain hare and ptarmi­gan are three fa­mil­iar Scot­tish species that turn white in win­ter.

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