Tracking down Suffolk's Hazel Dormice: 15 years of detective work

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MAMMAL CONFERENCE

TRACKING DOWN SUFFOLK’S HAZEL DORMICE: 15 YEARS OF DETECTIVE WORK SIMONE BULLION Hazel dormice are highly arboreal, native, small mammals primarily associated with ancient woodlands and hedgerows. Their exacting habitat requirements make them extremely scarce and consequently they are rarely seen in the wild. Occasionally, hibernating dormice are discovered during woodland management work such as coppicing. However, as there have been few such reports during the last decade, dormouse surveying is dependent upon locating their distinctive field signs. They make woven nests in dense vegetation in the shrub layer, usually out of stripped bark, but occasionally using tall grasses or sedges where available. This woven ball is then encased in leaves such as hazel or bramble. In addition, they also open hazelnut shells in a very distinctive way by creating perfectly round holes with a smooth edge, contrasting with wood mice and bank voles which also make a round hole, but with a chiselled entrance into the nut. However, in the absence of dense thickets where these aerial nests can be more easily found, or fruiting hazel providing an abundance of nuts, their presence can be extremely difficult to detect.

One hundred years ago, dormice could be found in most counties across England and Wales, with their distribution reaching as far as Yorkshire, Cumbria and Northumbria. It is likely that across much of this range they were already becoming scarcer and their populations fragmented, except across southern England where they are known to have been commonest. The current distribution indicates that there has been a significant contraction in range southwards, with populations being lost from all of the northern counties apart from Cumbria and also losses from the Midlands. As part of the Species Recovery initiative, a captive breeding programme (coordinated by The People’s Trust for Endangered Species (PTES)) has reintroduced populations at nineteen sites to date across the UK, including two in Suffolk.

In the Suffolk Victoria County History, Rope (1885) described dormice as commonest in the west central district and also in the woods around Belstead and Bentley. Julian Roughton conducted a ‘nut search’ on behalf of Suffolk Wildlife Trust (SWT) in 1986 and confirmed dormice were still present in two of the original ‘Victorian’ sites as well as recording their presence in six new locations. The Great Nut Hunt of 1993-4 (Bright et al., 1996) also confirmed their presence at two of these southern locations. Around this time, the dormice in the SWT reserve at Bradfield Woods were rarely seen, as investigated by Martin Hicks’ PhD fieldwork on the effects of coppicing on dormice.

By the time the author became involved in studying Suffolk’s dormice in 1998, they were only known at a single site in south Suffolk at Tiger Hill, Assington, so it was agreed that SWT would once again undertake a nut search using volunteers during the winter of 1998/99. This resulted in the discovery of a scattering of records in the south of the county within the parishes of Assington, Polstead and Bentley. In 2000, a captive-bred release took place into Priestley Wood in Barking and a regular monitoring programme started at this site using 200 wooden nest boxes.

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Torpid Dormouse (Photo: S. Bullion) In 2002, the Essex and Suffolk Dormouse Project was initiated, primarily through the vision of Robin Cottrill, who felt that cross-border collaboration would be valuable for sharing knowledge and skills. A new method for surveying using nest tubes devised by Morris & Temple (1998) was now available, so the group obtained a grant from Natural England to purchase several thousand nest tube ‘outers’ made from corrugated plastic, with the wooden inserts being constructed by our volunteers. For the next three years, they were used to find new populations in south Suffolk and also to assess the spread of the reintroduced population. We were extremely surprised to find good numbers of dormice in Bonny Wood (also in Barking) and the hedgerows connecting this wood to Priestley Wood, thus raising the query was this a result of recent colonisation or were they always there?

In 2005, Alison Looser joined the team to undertake a detailed study on the habitat requirements of dormice in hedgerows as part of her undergraduate dissertation (Looser, 2006). By using nest tubes she was able to build up a detailed picture of the distribution of dormice across an area in Polstead and link this to hedgerow diversity and structure.

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MAMMAL CONFERENCE

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In 2006, a second captive-bred release took place at Bradfield Woods, where there has been an unbroken history of coppicing since the eleventh century creating superb dormouse habitat. Although they had once been present, several years of survey had failed to find them, although the causes for this were unknown. Paul Bright, on visiting the wood, felt that this release should tell us something about dormouse ecology, whatever the outcome.

In 2008, Alison Looser took up a six month internship with SWT funded by PTES. As well as continuing nest tube surveys and finding new populations, she also started to assess connectivity through the landscape. We devised a ‘traffic light’ system for evaluating the quality of hedgerows and other landscape features, with ‘red’ indicating where critical links were either absent or not functional for dormouse movement. On the strength of this work, SWT was then awarded funding by Natural England as part of their Countdown 2010 ‘Halting the Decline of Biodiversity’ Project.

This allowed SWT staff to work much more closely with landowners to assess the quality of farmland habitat also to give advice on how to enhance habitats for dormice and other species. This was the start of a landscape-scale approach to dormouse conservation. We also had a small budget for hedgerow planting, so it was possible to start replacing critical linkages.

We were also interested in trying to locate any other remaining dormouse populations and felt that the density of ancient woodland remaining in the landscape was a key factor. Working with Suffolk Biological Records Centre and combining this data with information about the location of the original Victorian dormouse sites, this gave us a starting point for developing a ‘Predictive Mapping’ approach to trying to find ‘needles in a haystack’. In 2012, we secured funding from SITA Trust for a two year ‘Tracking down Suffolk’s Dormice’ project, thus putting this methodology into action. One of the most significant discoveries of this work was the confirmation that dormice are still present at Bulls Wood in Cockfield (one of the Victorian sites), despite earlier surveys giving negative results. This enabled a further year of funding

by SITA Trust to focus on a ‘Bradfield to Bulls Dormouse Corridor’, with a significant budget to improve connectivity between the two woods by planting hedgerows and a small copse as stepping stone habitat.

The high numbers of deer in Suffolk means that browsing of the new hedgerows is a serious problem. As well as protecting the young shrubs with spiral guards against rabbits and hares, the SITA Trust grant has also covered fencing of the new hedges to prevent deer-damage. The use of fencing increased the costs significantly, but was essential to ensure the survival of the plants.

The survey information we have amassed to date indicates that our Suffolk dormice are now distributed in five clusters based in and around the parishes of Assington, Polstead, Bentley/Belstead, Barking and Felsham/Cockfield. All other surveys outside of these areas have been negative. Given that a hundred years ago Rope described them as commonest in ‘the west-central district’, it appears that there have been extinctions within woodlands in this part of Suffolk.

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Nest tube surveys have revealed that dormice are rarely found in hedgerows more than 1.5km from ancient woodland. This helps explain why patches of habitat, although highly suitable in terms of structure and woody species diversity, if they are small and isolated will not support dormice. Where suitably connected by hedgerows, dormice can also colonise some quite unusual nearby habitats. These include conifer plantations, dense stands of bramble, the scrubby edges of disturbed habitats such as quarries and in scrub beneath power lines. It is highly likely that dormice cross small gaps on the ground in order to colonise new areas, although the frequency that this takes place requires further investigation.

Surveys are still continuing because, due to the difficulties of locating dormice, there may still be populations yet to be discovered. There is also regular monitoring of twelve sites by a team of licenced volunteers for the Dormouse National Monitoring Programme (NDMP). Data are submitted to PTES which coordinates this research project across the UK. This long-term monitoring work indicates that several of the populations in Suffolk exist at very low numbers. The cluster at Assington appears to be one of the most vulnerable, but the reasons for this are as yet unknown.

In recent years, we have been assisting research staff at Manchester Metropolitan University by collecting hair samples from the dormice under a specific project licence. The team in Manchester are then extracting and analysing DNA from the different clusters and it is hoped that this will increase our knowledge about genetic mixing and the effects of fragmentation and isolation. Early findings indicate that Suffolk’s dormice contain a unique haplotype, distinct from any other dormice in the UK (Fraser Combe, pers. comm.), implying that they have been isolated from the rest of the UK for a significantly long period. Such results pose interesting new questions surrounding the captive bred releases, as these were sourced from breeding stock across the UK. The implication of any future genetic mixing arising from the recently planted hedgerows is still unknown, but is believed to be neutral or even beneficial.

Reducing population fragmentation is still one of the main drivers in dormouse conservation, along with habitat creation and reinstatement of sensitive management of woodlands.

References Bright, P. W., Morris, P. A. & Mitchell-Jones, A. (1996). A new survey of the Dormouse Muscardinus avellanarius in Britain, 1993-4. Mammal Review, 26: 189–195.

Looser, A. E. (2006). A study of dormouse ecology and habitat requirements in the hedges of Polstead Heath, Suffolk.

Morris, P. A. & Temple, R. K. (1998). ‘Nest tubes’ – a potential new method for controlling numbers of the edible dormouse (Glis glis) in plantations. Quarterly Journal of Forestry, 92: 201–205.

Rope, G. T. (1911). Mammals. In W. Page. (ed) The Victoria History of the Counties of England. A History of Suffolk. Vol 1, pp. 215–233. Constable & Co., London.

Dr Simone Bullion Suffolk Wildlife Trust, Brooke House, The Street, Ashbocking, Ipswich, Suffolk IP6 9JY Simone.Bullion@suffolkwildlifetrust.org Trans. Suffolk Nat. Soc. 51 (2015)