Thick fur or feathers: Many animals that live in the north have thick layers of fur or feathers to help insulate them against the cold. For example, polar bears have fur that can be up to 4 inches thick, and they also have a layer of fat under their skin that helps to keep them warm.
Small bodies: Animals with smaller bodies have a higher surface area to volume ratio, which means that they lose heat more quickly than larger animals. To compensate for this, many northern animals have stocky bodies that help to minimize heat loss. For example, arctic foxes have short legs and ears, and they also have a dense layer of fur.
Hibernation: Some animals that live in the north hibernate during the winter months. Hibernation is a state of deep sleep in which an animal's metabolism slows down and its body temperature drops. This allows the animal to conserve energy and survive on the stored fat reserves until spring arrives.
Behavioral adaptations: In addition to physical adaptations, some animals that live in the north also display behavioral adaptations that help them to stay warm. For example, many animals huddle together in groups to share body heat, and some animals also build nests or burrows in the snow to provide shelter from the elements.
By combining these adaptations, animals that live in the north are able to survive in some of the coldest environments on Earth.