photo periodic pelage reaction

In the u.k there are four animals that turn white in winter,ptarmigan,mountain hare,stoat and the weasel. They do this to avoid predation from golden eagles in the cairngorms. Photo periodism- The eye records the local day lengths and this is the photo-periodism, they then communicate this information to the brain, which then relays it to their hormonal or the endocrym system. This then produce`s a compound called melatonin. This compound inhibits the production of pigments so when they moult the new feathers and fur come through white. The speed of change is not controlled by the day length but by the air temperature. They will go whiter quicker at higher altitudes. Because of genetic factors, Southern weasels and stoats couldn't`t go white anymore. There are microscopic sub structures of bubbles in the ptarmigans feathers to keep them warmer. Mountain hare`s coats are thicker in winter and when a stoat moults it goes whiter from the feet and belly first, This is because they are closer to the ground and it keeps the stoat warmer.The reverse happens in winter with the stoats nose going white first followed by the rest of its body down to its feet.