Dormice in Hedgerows

Dormice are one of our most distinctive and attractive native mammals, but despite frequently appearing on leaflets, magazines and interpretive material, their behaviour and habitat requirements are still poorly understood compared with some other mammals. They currently are found in the centre and south of Suffolk, with the majority of records occurring in the Stour Valley. Historical records from the Victorian County Histories indicate a very similar distribution, except that dormice were frequently encountered in the area between Bury St Edmunds and Sudbury, where there are now few records.

Traditionally, dormice are a woodland species and some of the best conditions for them are found in ancient, semi-natural woodland where hazel is coppiced on a long rotation. However, loss of woodland and fragmentation of remaining habitat, along with abandonment of coppice management has led to increasing isolation and vulnerability of their populations or even extinctions in other counties. Hedgerows also provide important habitat for dormice as they act as food producing dispersal corridors or as permanently occupied habitat in their own right.

So why are dormice so vulnerable? One reason is that they are compromised by our oceanic climate of mild winters and warm, wet summers, which means that in Britain they are on the edge of their range. They are also arboreal specialists, who don’t like coming down to the ground (except to hibernate). As a consequence of this they require a continuous, vigorous shrub layer to aid aboveground movement (i.e. good structure) and they also need a species-rich mix of shrubs and trees (diversity). Their requirement for the latter is related to their internal biology, which demands a high quality diet.

Dormice are therefore dependent on a variety of different food sources during the year. In spring, they feed on the pollen and nectar from flowers. Many species are visited, but honeysuckle and bramble are particularly important. In summer there are few flowers and the autumn fruits and nuts are not yet available, so they feed predominantly on insects (caterpillars and aphids) in trees and shrubs such as oak and hazel, which have a high biomass of insects. In the autumn there is plenty of berries (soft mast) and nuts (hard mast) available. Many species are eaten but hazel and a range of soft fruits, particularly bramble, are important.

Dormice open hazel nuts in a distinctive way, leaving a round hole with a smooth inner rim. They also make distinctive nests, but these can be harder to find.

Where dormice are known to occur, nest boxes can be placed at regular intervals to record the animals themselves at close quarters. This can provide important population data but does require an English Nature licence because of their protected status. It is more difficult to study dormice in hedgerows because it can be difficult to find evidence of their presence, particularly where hazel is absent.

A new method, recently devised by researchers at Royal Holloway College, University of London, consists of a square tube of tree guard material and a wooden insert. These nest tubes are suspended underneath horizontal branches and they have been found to be very attractive to dormice. When a dormouse takes up residence it makes a nest. This can appear as a ball of fresh leaves or a woven mass of stripped honeysuckle bark, or a mixture of both.

We are using these tubes in a number of hedgerows within Suffolk. The aims of this project are to locate areas used by dormice, estimate their density, and look at opportunities for dispersal and also the effects of management. At one site we are also investigating whether dormice prefer using the tubes to boxes. To demonstrate how we are studying the effects of management, at one study site it has been necessary to cut back the hedgerows to allow fencing prior to grazing as part of an ESA management agreement. We monitored the dormouse population prior to work taking place and found six animals along an approximately 600m stretch and subsequently we have already recorded three animals, with additional monitoring to follow. At another site, a network of hedges links two ancient woodlands and we are studying the movement of dormice within the hedgerows and between the woods. We are also interested to record how hedgerow management at this farm, under the Countryside Stewardship scheme, may be benefiting the dormice. We are also monitoring dormice in hedgerows between Priestley and Swingens Wood and the SWT’s own Bonny Wood. Dormice were reintroduced to Priestley Wood in 2000 as part of English Nature’s Species Recovery Programme. The tubes are a valuable tool to evaluate the potential for dispersal from the reintroduction site.

There is a certain urgency about this work. On a national scale dormice have declined in hedgerows by 70% in the last 25 years and these losses relate to intensive and frequent management. Hedgerow height and width have been found to be important and hedgerow management can influence food availability in the long term. Flailing has been found to particularly detrimental to soft fruit production (Bright and MacPherson, unpublished report). The bottom line is that uniform and intensively managed hedgerows cannot support dormice.

The loss of dormice from hedgerows is of high conservation concern. They are an indicator of biological diversity – basically good habitat with dormice will support a lot of other species, so in effect they are a ‘flagship species’. Research has also shown that dormice live at similar densities in hedgerows as in woodlands, so loss of dormice from hedgerows reflects a significant population loss. Finally, their loss will increase the isolation of remaining populations and may lead to localised extinctions.

We are addressing these issues by a programme of surveying to find the remaining hedgerows with dormice. We are also seeking to advise on appropriate management and to reinstate lost hedgerows to provide connectivity wherever possible. Clearly there are real opportunities through agri-environment schemes to implement good practices.

Finally, many people are involved taking this work forward. I would like to express may thanks to Paul Bright for sharing unpublished research material and to the Vaughn Bursary for assisting with funds. I am also grateful to the landowners who have given permission for me to rummage about on their land and to the numerous volunteers who have helped with this project. I am particularly grateful to Alan Rogers, Mike Ewart and Peter Mudd who have given much of their time and expertise to move things rapidly forward. I would also like to mention the setting up of a new initiative – The Essex and Suffolk Dormouse Project – which will be able to progress and coordinate dormice work within the two counties. It is my hope that in a year or two we really will be able to translate action into achievement.

Dr Simone Bullion
Suffolk Wildlife Trust

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