The number of dormice, also called dormice, is decreasing.
Since the turn of the century, dormouse numbers have declined by more than a third until 2016.
Experts believe the small mammal is under threat due to habitat loss, changes in the way forests and countryside are managed, and climate change.
Two cute hazel dormice in hibernation. After accumulating their fat reserves in the fall, hazel dormice go into hibernation in the winter. As the weather cools, they move from the trees to ground level, creating a tightly woven nest about the size of a tennis ball. They will curl up in this ball with their tail wrapped around their face and body to keep warm
Hazel dormice were once widespread in England and Wales, but have disappeared from 17 counties since Victorian times.
Now they are only commonly found in the south of England and in areas on the England-Wales border.
It is believed that there are only 45,000 hazel dormice left in the country, down from around 60,000 sixteen years ago.
According to the People’s Trust for Endangered Species (PTES) State of Britain Dormice report, numbers have fallen by 38 percent since 2000.
The current rate of decline equates to a 55 percent decline over 25 years, the report said.
The dormouse lives in low densities and would therefore not be the garden mouse’s main prey.
‘Introduced gray squirrels pose a much greater threat and are known to eat both young dormice and limp adults,’ Hazel Ryans, senior conservation officer at Wildwood Trust, told MailOnline.
‘Even our native yellow-necked mice have been known to kill and eat the brains of dormouse.
‘(But) in some parts of Europe, for example Poland, the hazel dormouse and the dormouse are both native and live very happily together.’
Hazel dormice can occasionally be seen roaming the countryside in search of food.
Agile climbers and mainly nocturnal animals, they are very rarely seen.
They live in woodlands, hedgerows and dense shrubs and can spend their entire lives in the branches without ever touching the ground.
The species eats buttons, hazelnuts, berries and insects.
It builds summer nests from the bark of the honeysuckle, in which the female can give birth to up to seven young.
They hibernate during the winter months, in a dense nest built in a tree hollow or similar sheltered spot, curling up into a cute ball.
Dormices thrive in shrubby habitats and brambles, and use hedgerows to move around the countryside.
One of the biggest threats to the small animals is a lack of forest management, which leaves trees unruly and isolated.
They have also been affected by more intensive farming, which has led to the loss of hedgerows and ‘flail cutting’, which reduces suitable habitats.
Ian White, dormouse officer at PTES said: ‘Forests across the landscape are becoming increasingly isolated. Dormice need the hedges to move around.
‘The problem within our fragmented landscape is that dormice have become locally extinct in a forest, and without a hedge network it is difficult for them to get back there.’
Mr White added that climate change is also impacting mammals, which hibernate in winter.
Hazel dormice, their breeding sites and resting places are protected by British law.
The UK government says: ‘You may be able to obtain a permit from Natural England if you cannot avoid disturbing them or damaging their habitats.’