SEASONAL COLOUR CHANGE
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.