# Hazel Dormouse (Muscardinus avellanarius)

- Web page: https://www.funwildfacts.com/norden/mammal/hazel-dormouse
- Published: 2026-05-30
- Last updated: 2026-05-30

## Overview

The hazel dormouse is one of Europe's most charming and elusive small mammals. Despite its name, it's not actually a mouse but belongs to the dormouse family (Gliridae), more closely related to squirrels than true mice. With its golden-orange fur, large black eyes, and fluffy tail, this tiny creature looks like a miniature squirrel. Weighing only 15-40 grams and measuring 6-9 centimeters in length, plus an equally long bushy tail, the dormouse is perfectly adapted for life in the shrub layer of woodlands.

This nocturnal animal is famous for its extraordinary sleeping habits – the hazel dormouse can spend up to seven months of the year in hibernation! From October to April, it curls up in a carefully constructed nest on or just below the ground, where its body temperature drops dramatically and its heart rate slows from 350 beats per minute to just 4-10 beats. During this time, it survives entirely on fat reserves built up during summer and autumn by eating nuts, berries, and insects.

The hazel dormouse is an excellent climber that rarely descends to the ground. It uses its agile paws and prehensile tail to navigate through dense shrubs and low trees, where it searches for food and builds its characteristic round nests from grass, moss, and bark. The species is particularly associated with hazel bushes, which explains both its common name and its Latin name (Muscardinus avellanarius, where 'avellanarius' comes from the Latin word for hazel).

Unfortunately, the hazel dormouse has declined dramatically in many European countries due to habitat loss and fragmentation of woodland areas. In Britain, it has become a priority species for conservation, and in Scandinavia it's found mainly in the southern regions. The species is protected under the EU Habitats Directive and is considered vulnerable across much of its range.

## Quick facts

- Weight: 15–40 g
- Length: 6–9 cm
- Lifespan: 3–5 yrs
- Diet: Herbivore
- Conservation Status: Least Concern

## Habitat

The hazel dormouse thrives in dense, species-rich deciduous woodlands and scrubland with good availability of hazel, birch, oak, and other broad-leaved trees that produce nuts and berries. It prefers older woodlands with rich undergrowth where various shrubs and trees form a dense network of branches at different heights, allowing it to move through the forest without needing to descend to the ground. Forest edges, ancient hedgerows, and abandoned orchards are particularly favored habitats.

In Scandinavia, the hazel dormouse is found mainly in southern Sweden and Denmark, where the climate is milder and deciduous trees more abundant. The species requires environments with a diverse seasonal food supply – pollen and insects in spring, berries and fruit in summer, and nuts in autumn to build up fat reserves for winter. Unfortunately, modern forestry and agriculture have fragmented many of these habitats, making the hazel dormouse increasingly rare across much of Europe.

- Forest
- Woodland
- Heathland
- Garden
- Farmland

## Seasonal Behavior

The hazel dormouse's year is clearly divided into active and inactive periods. From April-May it awakens from hibernation and immediately begins searching for food to recover from the weight loss during dormancy. During spring, it eats mostly pollen, buds, and insects. From June to September is the breeding season, when females can have one or sometimes two litters of 3-7 young. During autumn, the consumption of nuts and berries intensifies to build up vital fat reserves. In September-October, the dormouse prepares its winter nest and enters hibernation, where it remains motionless until spring returns.

## Breeding

- Gestation: 22 days
- Offspring: 3–7 

## Behavior & Ecology

- Activity Pattern: Nocturnal
- Social Behavior: The hazel dormouse is a distinctly solitary animal that only seeks out conspecifics during the breeding season.
- Migration: Resident
- Population: Declining in many areas, estimated several million individuals across Europe

## Did you know?

- The hazel dormouse can sleep for up to seven months each year – longer than almost any other European mammal!
- Unlike common mice, dormice have no unpleasant smell – in fact, they have a rather sweet, mild scent.
- When eating hazelnuts, the dormouse gnaws a perfectly round hole with a smooth edge in the shell – experts can identify the species just by looking at nut shells!
- During hibernation, a dormouse's body temperature can drop from 35°C to just 1-2°C without harming the animal.
- The hazel dormouse is the only dormouse species still living in Britain, where it has become a symbol of wildlife conservation.
- It can climb upside down on thin branches thanks to special foot pads that provide extra grip.
- The dormouse wakes up several times during winter to eat from its hidden food stores and to urinate – otherwise its bladder would burst!
- In Alice in Wonderland, a dormouse appears at the Mad Hatter's tea party – inspired by the hazel dormouse's reputation for being perpetually sleepy!

## Taxonomy

- Kingdom: Animalia
- Class: Mammalia
- Order: Rodentia
- Family: Gliridae
- Species: Muscardinus avellanarius

## Image

- URL: https://images.djurfakta.com/animals/hasselmus/1777853711479-1.jpg
- Photo: Danielle Schwarz
- License: CC BY-SA 3.0

## Other languages

- sv: https://www.djurfakta.com/norden/mammal/hasselmus
- da: https://www.dyrefakta.com/da/norden/mammal/hasselmussvale
- no: https://www.dyrefakta.com/norden/mammal/hasselmus