Some of these migrants fly at night, particularly the smaller ones. It is a breathtaking sight to see the dark figures of a flock of birds migrating at night against the moonlight. For an animal to survive in winter, it must be able to find food, keep its torso above freezing, and maintain that warmth. Some animals shiver to produce heat. The chickadee may shiver continuously throughout the winter.
Feathers are good insulators because they help the birds trap warm air around their skin.
Other animals prepare for winter by getting out of the cold. Not all animals are true hibernators, but the groundhog, also known as the whistle-pig , or the woodchuck , is an exception. The groundhogs eat enough all summer long to have fat reserves for the winter. They do not store food in their burrow so they have to eat enough to sustain them throughout the winter. Deep in their burrows, which is a system of tunnels and chambers, the groundhogs are rolled into a tight ball with their head between their hind limbs.