A female Eurasian red squirrel carrying moss, Switzerland

Twig by twig, she prepares. A Eurasian red squirrel in Switzerland

Quick, clever, and always on the move—meet the Eurasian red squirrel, a leafy treetop resident found across much of Europe and Asia. While it prefers the shelter of forests, this agile creature easily adapts to gardens and parks. It builds its nest, called a drey, high in the fork of a tree using twigs to form a domed structure about 10 to 12 inches wide. The female featured here is gathering moss—one of several soft materials, along with bark, leaves, and grass, that line the nest and turn it into a snug, well-insulated retreat. These rodents may also take over tree hollows or abandoned woodpecker holes when available.

Typically solitary and quite shy, they rarely share food or space. However, during colder months, it's not uncommon for several individuals to use the same nest to stay warm. Their social organization is shaped by dominance hierarchies, both within and between the sexes. While males aren't always dominant over females, the top-ranking individuals tend to be older and larger. Dominant males also tend to occupy larger home ranges than subordinate males or most females.