The Hazel dormouse (Muscardinus avellanarius) is a nocturnal dormouse that lives in understory-rich woodlands across Europe. It is small-bodied with a bushy tail and primarily feeds on the nuts and fruits of hazel and related plants, flowers, and insects. From about October until the following spring it undergoes a prolonged hibernation, during which its hibernaculum forms a roughly spherical nest about 9 cm in diameter. Breeding occurs from spring through autumn. Populations show declines in some regions and therefore require attention, but overall the species is classified as Least Concern.