The Elusive Hazel Dormouse

©Jack Hawnt

Hazel dormouse, their ecology, conservation status and monitoring.

Now that the surveying season is in full swing, the Arcadian Ecology team at the Hampshire & Isle of Wight Wildlife Trust are extremely busy getting an array of important ecological surveys underway and completed.

One of these key surveys is monitoring the presence of an adorable, but fairly elusive rodent known as the hazel dormouse.

Hazel dormouse in torpor

©Jack Hawnt

About dormice

Name: Hazel dormouse (or just dormouse) (Muscardinus avellanarius)

Taxon: Rodentia

Length: 6-9cm 

Tail: 5.7-6.8cmWeight: 15-40g 

Average lifespan: 5 years

When to see: April to October

Distribution: Mainly southern England & Wales

Habitat type: Coniferous woodland, deciduous woodland and mixed woodland.

Diverse coppiced woodland with heterogeneous structure is preferred, as this allows for food to be available throughout the summer.   

Key features to look out for: distinctive ginger brown-fur, large, black bead-like eyes and a long fluffy tail.

Trainee Ecologist Jack Hawnt assisting with a dormouse survey

Trainee Ecologist Jack Hawnt assisting with a dormouse survey

©Sarah Boswell

Ecology

The reason that dormice seem so elusive, is that they are a strictly nocturnal species, meaning they usually only come out at night. The dormouse tends to stick to staying high up in the trees, climbing from branch to branch in search for food and rarely coming to ground. So during the day the dormouse will spend its time asleep in a nest either snug up in a tree hollow, or in a nest box like the ones we use in our surveys. To conserve energy when weather conditions or food supply is short, dormice can reduce their body temperature and go into a state of semi-hibernation known as torpor. However during the winter, a dormouse will go into full hibernation and will not awake and become active until April-May.

Conservation status

Surveys for this decade have shown that the dormouse is in a steady decline, with reasoning being put down to the loss of ancient woodland, coppice management and fragmentation. This is why there is such an importance put on in ecology for monitoring their presence and numbers. In order to aid in protecting their remaining numbers the dormouse is listed under the Wildlife and Countryside Act, 1981. Meaning they are protected by law and may not be intentionally killed, injured or disturbed, collected, trapped or sold unless under licence. In order to handle a dormouse you must be a licensed individual or in the presence of someone that holds one.

Monitoring on our reserves

With the South of England being a stronghold for remaining dormouse numbers, many of our reserves at HIWWT have dormice present. To monitor numbers and the population health, as well as advising and putting into place future habitat management strategies, the ecology team use a surveying technique of specially designed nest boxes. These boxes differ from a bird box as the hole faces the tree, rather than outwards. These boxes are then checked regularly by our licensed individuals, where we record the dormice's sex, age, weight and number found. 

So far this year I have been on three dormice surveys, and have been lucky enough to see them in their current torpid state, all of which feature in the images shown on this blog. Soon enough the dormice will be active, which makes surveying a little more tricky as they are known to jump out of the boxes! 

Dormouse box

Trainee Ecologist Kate Gwynn and Ecologist Sarah Boswell putting up dormouse boxes for a new survey site on the Isle of Wight

©Jack Hawnt