The mating season of Hazel Dormice is not very clear and it is suggested that mating depends very much on the weather. If the weather is too cold or severe, Hazel Dormice go into ‘torpor’ which is a state of sleep. However, it seems that most mating occurs around June.
The female Hazel Dormouse is pregnant for approximately twenty-four days. During this time she builds one or more breeding nests to bring up her young in. She builds several breeding nests just in case the nest she is using is disturbed by predators or humans. If this happens, she will move her young to another nest.
The female Hazel Dormouse usually gives birth to a litter of three to five young between July and August. Sometimes she gives birth to a second litter in September. The young of the second litter don’t usually survive because they don’t have enough fat reserves to live off during hibernation.
The young are born blind and naked. They are a pinky colour and only weigh three to four grammes each. Their fur starts to grow after a week and within two weeks they have full coats of fur. The young Hazel Dormice start to open their eyes when they are approximately three weeks old. The mother provides them with milk and grooms them regularly.
After twenty-four days the young start to look like miniature adults, but their fur is a greyer colour. The young Hazel Dormice leave the breeding nest after about thirty days and build ‘shelter nests’. Shelter nests are built fairly close to other shelter nests. Each nest is occupied by a single young Hazel Dormouse. Shelter nests are smaller than adult nests.
The young do not develop a coat of fur like their adults until they have had their first hibernation. After their first hibernation, they also become sexually mature. This is the time that they too may have young of their own and so the cycle of life begins again.