The hazel dormouse hibernates from October until roughly April–May.
It usually spends the cold season in a nest on or near the ground, tucked beneath leaves, logs, roots, tree stumps, or dense vegetation. These sheltered locations reduce exposure to sharp changes in temperature and humidity while the dormouse’s metabolism and body temperature fall.
When it wakes in late April or early May, the animal returns to its largely arboreal lifestyle. It builds woven summer nests from materials such as honeysuckle bark, fresh leaves, and grasses, then feeds on flowers, insects, berries, and nuts as the breeding season begins.
The dates are approximate because local weather and food supply affect both entry into and emergence from hibernation. Hazel dormice also use shorter bouts of torpor in summer when cold, wet weather or scarce food makes activity energetically expensive. They are not the same species as the larger edible dormouse, which follows a somewhat different seasonal pattern.