Dormouse Monitoring

Dormouse Monitoring in Cardiff

With their large black eyes, fury honey-coloured tail and tendency to curl up into little balls for naps in cold weather, the hazel dormouse is surely one of the most loved of all our British mammals. Unfortunately, due to their nocturnal behaviour, secretive lifestyle and the fact that they can sleep for up to seven months of the year, very few people get a chance to ever see these charming creatures.

Some of the staff members at Acer Ecology have been involved in a long-term dormouse project in Cardiff, as part of the National Dormouse Monitoring Programme (NDMP).

Once a month between April and November, we meet up with other dormouse surveyors at the Howardian Local Nature Reserve, near Newport road in Cardiff. The ‘Friends’ of Howardian LNR have set up 52 dormouse nest boxes across the site and have been monitoring the dormouse population there for over 10 years. Several of the Acer staff possess personal survey licences for dormice (we carry out dormice surveys across England and Wales regularly), and, together with Gerry and Martin from the ‘Friends’ group, we carefully approach each box, before plugging the entrance hole and carefully removing the lid to check the contents. After peering inside, if we suspect that the box may contain dormice or a dormouse nest, we carefully transport it into a large polythene bag before inspecting it further.

It is important to ensure that any dormice that may be present do not escape into the adjacent vegetation. Dormice fur is not waterproof, which means that they are susceptible to becoming chilled in wet weather (although surveys during heavy rain are avoided). Furthermore, dormice are at an increased risk of predation during daylight hours, so it is important to make every effort so that they do not escape during the visits. Any individuals that we find are weighed and sexed, before being posted back into the box.

A ‘classic’ dormouse nest is very distinct. It comprises an outer shell of Dormouse Nestfresh green foliage (typically hazel), with a tightly woven inner-core of stripped honeysuckle and bark. The contents are usually very dry and odourless. This structure, and the preference for fresh green foliage, easily distinguishes it from the nests of wood mice (which typically comprise loosely sorted damp, brown foliage).

We often also find a range of other animals using the boxes, including wood mice, pygmy shrews and nesting birds! Although we have not found any ourselves, dormice surveyors sometimes discover roosting bats within the boxes too.

Howardian LNR lies within the lower Rhymney Valley of Penylan, Cardiff. It is a wildlife oasis of woodland, wildflower meadow, ponds and reedbeds, right in the heart of the capital. The 32-acre (13 hectares) reserve is only a mile and a half from Cardiff’s city centre. Remarkably the reserve was a domestic refuse tip in the early 1970s. Although a large proportion of the site had been used as a landfill site, much of the relict estuarine vegetation still exists and forms a major feature within the Reserve. The ‘Friends’ Group was formed in 1989 by an enthusiastic group of local residents. They work with Cardiff County Council to further improve the Reserve. Works continue today to develop Howardian LNR for its wildlife interest and public enjoyment. A good network of paths now weaves between the great variety of habitats that are packed with interesting flora and fauna. Interesting plants include Bee Orchid, Common Spotted Orchid, Southern Marsh Orchid and Butterfly Orchids, Twayblade, Broad-leaved Helleborine, Grass Vetchling and Celery-leaved Buttercup.Dormouse Survey Newbury

Incredibly, for a nature reserve within the heart of Cardiff, Howardian supports a population of dormice. This population is thought to be a relic population from the network of ancient hedgerows and farmsteads that once lay in place of the city centre (one of which still lies within the site). The dormice population within Howardian likely became isolated during the urbanisation of Cardiff, but the high-quality habitats within the site mean that they have been able to survive as a viable long-term population. Monitoring the population here has enabled the ‘friends’ to better understand the dormice here, and to better manage the site to support their survival.

The hazel dormouse is an ancient, native species; it has been present in Britain since at least the last Ice Age, more than 10,000 years ago. They were so prolific in Victorian times that school children would trade them in the playground. Indeed, Beatrix Potter kept a hazel dormouse (Xarifa) as a pet.

Dormice tails are 80% of their body length. Uniquely, they boast double-jointed hind ankles, which enable them to easily navigate dense scrub and woodland canopies. Dormice lack a caecum, which means they cannot digest green plant material. They are therefore reliant on a range of flowers, fruits, nuts and insects throughout the year. As the name suggests, they have a particular penchant for hazelnuts. It takes a dormouse 20 minutes to open one hazelnut – leaving a distinct set of marks around the rim of the hole.

Unfortunately, dormice face many threats and have declined dramatically across much of their range in Britain. Originally dormice were widespread over most of England and Wales, but they are now only really found in the south and west (a few isolated populations exist in the north-west). Dormice are slow breeders and poor dispersers and generally live in older woodlands with a well-developed understory often linked by old hedgerows. In the majority of woodlands in Britain, the management required to maintain a well-developed understory has ceased, 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. The future effects of climate change on dormice is unknown.

The NDMP collates and inputs the records from around 400 dormouse monitoring sites across the UK. It has been running for the past 25 years and has several hundred trained monitors responsible for organising surveys – using dormouse boxes throughout the year.

Why not get involved!

Dormouse monitoring is a great way to improve your skills, meet like-minded people, or just an excuse to get out into the woods! Anyone can take part, so it’s worth getting in touch with your local mammal group to find out about dormouse survey sites near you! The ‘Friends’ of Howardian are always happy to support volunteers at this wonderful nature reserve.

Find out more about the people that work for Acer at:

We are always interested to hear from qualified, experienced and highly motivated ecologists who would like to join our team – See our current vacancies, or email us at