Several mammalian species turn white for the winter. On the other hand, there is only one species of bird that has this behaviour: the ptarmigan.
The ptarmigan is a member of the pheasant family. It exchanges its brown and grey summer plumage for a white coating during the winter, only the tail feathers remain black. It is a bird that lives in the Alps and can also be found in the Pyrenees. During the winter, this white plumage will allow it to escape its predators: the fox and the golden eagle, and to concentrate on searching for food. Thus, thanks to this phenomenon, the strategy of this bird is to survive its predators.
As for the mammals that turn white in winter, you can find Arctic foxes, mountain hares, ermine... There are about twenty of them!
The change in coat colour takes place in a few months and begins in autumn to prepare for the coming winter. The animals most concerned are those living in cold regions such as the Arctic Circle.
The reason for this phenomenon is mainly camouflage. Camouflage has a double function: to hide from predators and/or prey, as is the case for the Arctic fox, which then becomes a formidable hunter in snowy landscapes.
For some animals, this change in coat also means a thicker coat, which is much more effective at insulating themselves from the cold.
The triggering factor for this process is a reaction to photoperiodism, which is the ratio between the length of day and night. In autumn, the animals observe the shortening of the day length and a reduction in light that will trigger the emergence of the white coat. The opposite phenomenon is observed at the end of winter, a lengthening of the days will trigger the reverse cycle and the loss of the winter coat.
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