It's autumn in Scotland and the clock is ticking. As daylight diminishes and the weather cools, food resources dwindle. Animals must either migrate now or prepare to face the winter head-on.

It is late January and in the western Highlands of Scotland, and it's unusually warm, even at night. The warmth has brought red deer out of hiding. With no snow or bitter winds to contend with, they're heading back to the hilltops.