Hazel dormouse
I don’t think I could ever live somewhere for a long time where there are no definite change in the seasons. I love the green flush of spring with the feeling of anticipation of what is to come, the long summer evenings watching the bats hunt in twilight, the change of colours in autumn, and the biting cold and the cozy feeling of getting home after a long day in the field in the winter. With that in mind, it has made me think of a species that decides to opt out and hibernate through the winter months: the hazel dormouse (Muscardinus avellanarius).
This minute, elusive endangered species, which is quite adorable – even a hardy ecologist like me can admit that – with a body length of just 6-8cm and a long, feathery tail with a similar length. They have golden fur with big black eyes and weigh next to nothing – no more than 40g.
Dormice are a nocturnal arboreal species, spending nearly all their time with their feet off the ground in the woody vegetation of mixed deciduous hazel coppiced woodland, old hedgerows, scrubland and occasionally conifer woodlands. They can be found in old and new coppice, preferring the new growth that arises after woodland management such as coppicing, ride widening, thinning or glade creation. Their range has shrunk significantly, and they’re now confined predominantly to southern England, with a few scattered populations in the Midlands, Wales and Lake District. Even where dormice remain, their distribution is patchy.
They have a varied diet depending on the time of year; in autumn, they will feast on nuts such as hazelnuts, along with seeds and berries, which enables them to put on enough fat to survive hibernation during the winter. Once they emerge from hibernation, they will eat the blossoming flowers of trees such as hawthorn and oak, also taking insects like caterpillars when summer arrives.
As part of a work placement during my first year of my degree, I had to go through dozens of bin liners full to the brim of chewed hazelnuts from woodlands all over the county. It was part of a project in Hampshire to establish which woodland had dormice present, using a survey method that was low impact. Did you know that one way of figuring out if you have dormice in your woodland is by inspecting each opened hazelnut? (And I have inspected thousands and thousands of them in my time!)
Each mammal species opens a hazelnut in a different way – for example, a squirrel will just bite straight through the nut and the cast shell will be quite jagged; a wood mouse opens the nut by biting a circular hole with bite marks that are vertical like the edge of a coin; but the dear little dormouse has a more delicate, distinctive way of getting into the nut. It opens the nut by gnawing a little round hole, leaving circular bite marks that run parallel with the edge of the hole, with a few marks left on the edge of the nut.
Dormice have been found sleeping in nests and nest boxes, but generally they weave their own nests (often in brambles or other shrubs) from strips of honeysuckle bark or a similar plant, surrounded by a layer of green leaves. They usually have a single litter of four to five young each summer, which are born pink, completely hairless and blind. By the time they are 12 days old they are covered in pale grey fur, and they can see after 18 days. The young begin foraging with their mother at around three weeks old, leaving the nest after roughly six to eight weeks. Their fur stays grey until they are around a year old and sexually mature, when it changes to a golden-brown hue.
After gathering up their fat reserves in autumn, hazel dormice will begin hibernation in winter for up to seven months. Dormice move down from the canopy to the woodland or hedgerow floor and create a tightly woven nest around 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 between October and May, beneath the leaf litter.
Even during periods of cold weather or low food supply outside of winter, hazel dormice can actually go into a state of deep sleep called ‘torpor’, similar to hibernation, to conserve energy.
The reason for the decline of this species is the loss of ancient woodland and hedgerows across the UK, as dormice will not leave the safety of trees to cross large, open spaces. This means populations become isolated, lose genetic diversity, and are therefore more vulnerable to extinction. This, coupled with a reduction in traditional woodland management, such as coppicing, has also impacted the species’ numbers. A coppice rotation of woodlands creates ideal habitats for dormice, but this is being implemented much less frequently nowadays. It is also thought that climate change is another big threat to the hazel dormouse. As the winters become milder, they disrupt the species’ hibernation cycle, meaning dormice wake early when sufficient food isn’t available.
Dormice are slow breeders and poor dispersers, and generally live in older woodlands with a well-developed understory, often linked by old hedgerows. Generally, the majority of woodlands in Britain are not managed in a way to develop a good understory, making them less suitable for dormice. Inappropriate management of hedgerows, or their removal, has meant that woods that have lost their dormice will not be repopulated, as they cannot get to them and the effects of climate change are still unknown.
What can we do?
To conserve this species, we need more well-managed, species-rich connective hedgerow habitat across the landscape, and well-managed deciduous woodlands. By linking up well-managed hedgerows and woodland with your neighbours, it will enable the dormouse to move farm to farm, woodland to woodland, increasing its range and repopulating areas where it might have once been.
While you out this winter, coppicing your woodland or just out for a walk, pick up a few hazelnuts to see if you have this wonderful but endangered species on your doorstep, and think about what you can do to increase its chances for the future.
Megan Lock
Advisory
Image credit: Jan Ebr & Ivana Ebrová