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Hazel Dormouse

Hazel Dormouse by Archibald Thornburn

The Hazel Dormouse Muscardinus avellanarius is a distinctive native British mammal but is uncommonly observed due to its rarity and nocturnal habits. Nationally, it has declined in both numbers and distribution over the last 100 years, with recent surveys suggesting it has become extinct in about half its former distributional range, including six counties where it was reported to be present by Rope (1885). There are also fewer than 10 known sites north of a line between the Wirral and the Wash (including recent reintroductions). The most northerly location is along the river Allen, near Hexham in Northumberland, with at least three more sites in Cumbria.

Dormice are now either absent or very thinly distributed in most midland counties, although they have been found in a few widely separated areas in every county of Wales, except Anglesey. Although still uncommon, the dormouse appears to be relatively widespread in the southern English counties, but even here it has a very patchy distribution.

The Hazel Dormouse is easily overlooked, even where present, as it is rarely caught in traps or by predators, spends much of its active time high off the ground and at least a third of the year in hibernation, making it even more unlikely to be recorded by the casual observer.

It is associated with deciduous woodland, but also occurs widely in species-rich hedgerows and scrub. Their specialised feeding requirements mean they are never as numerous as other woodland rodents. They are also especially sensitive to weather and climate with habitat deterioration and fragmentation combining to make them highly vulnerable to local extinction.

The history, status and distribution of the dormouse in the North East is extremely poorly recorded, although distribution maps from recent national surveys show Northumberland as the northern limit of the species distribution. The most comprehensive account of the status of Hazel Dormouse in our region was produced by Coult (2001), in which the author states “Contrary to national survey results the locally published records suggest that the dormouse once had a distribution, which encompassed all of the main river valleys within County Durham. Records exist for the valleys of the rivers Derwent, Tyne, Wear and Tees, with records extending into the twentieth century in the valleys of the Tyne and Derwent. The oldest dated record is from the Derwent Valley, the ‘near Ebchester’ specimen, in Mennell and Perkins was collected in 1829.”

Records for Northumberland are sparse with only the Tyne Valley at Stocksfield and the Allen Valley providing published records. The extract from Bolam’s diary (1921) provides a history of records stretching from 1914 to the present for those sites in the Allen Valley where dormice were found during the Mammal Society Survey in 1975-79.

The preparation of this account involved a comprehensive search of archival material for records of Dormouse and these were found to be infrequent, suggesting that the species has always been uncommon in our region.

Most recent national surveys (Great Nut Hunt 1994 and Victorian Nut Hunt 1997) failed to produce evidence of Dormouse across Durham, although the latter produced three, closely-related sites in Northumberland, which were subsequently included as part of the National Dormouse Monitor Scheme. This scheme recorded dormice occupation of nest boxes until 2006. No evidence was recorded in 2007 and 2008, at which point checking appears to have ceased. However, a recent check of nest boxes in the area (2012) produced a single unoccupied nest (formed principally from woodrush) which was thought to be fashioned by a dormouse. It is interesting to note that this site is close to the earliest Northumberland record at Whitfield (Bolam, 1921).

A number of recent unverified records have been reported in woodlands close to Stocksfield and Wylam. This area coincides with one reported in Cowan (1975) and subsequent reports made by reliable field naturalists. This suggests that additional field-work may be worthwhile in this area, which retains good quality broad-leaved woodland.

The most recent Durham record, albeit unverified, was at Lockhaugh, Rowlands Gill from D. Smith in 2001. Subsequent survey of nest boxes placed there (and at Hareshaw Linn, Northumberland) by the reporter failed to produce any evidence of occupation.

Records for Cleveland are also extremely limited. The species is listed in the appendix of Graves (1808) but this does not specify a location. Rope (1885) lists it from several places along the northern boundary of what is now the North York Moors National Park, from Pinchinthorpe to Grinkle Park, and reports that Mr T.H. Nelson considered it not numerous near Redcar. Rope also cites a record from Headlam, close to Darlington, of a pair of dormice that frequented a peach tree until one of them drowned in a bottle of beer hung on the tree to catch wasps. Cleveland has not been included in any of the recent national surveys, presumably due to a lack of contemporary records. However, nest tubes have more recently been erected in two woodlands (Cow Close and Hagg Wood) where the species is remembered by local naturalists from the 1970s (Kenny Crooks, pers. comm., 2010), although these have not produced any new evidence to date.

Dormouse is infrequently reported within the region and records are not usually supported by evidence (photographs, corpses, nests, etc.). As a result many records are considered to be misidentifications, usually of Wood Mouse Apodemus sylvaticus. However, given the difficulty in surveying for the species it is possible that additional isolated populations may occur in areas of suitable habitat. In such circumstances the potential for re-introductions may be considered.

MARS Hazel Dormouse

There is a close association of Dormouse records with ancient woodland sites, many of which are likely to have undergone significant change, especially in recent years. Certainly Dobson (2000) suggests that many former haunts may have been clear-felled during both World Wars, making many areas unsuitable for the species and increasing the fragmentation of habitat, severely limiting its capacity to colonise new areas.

However, the distribution of Hazel Dormouse in Durham and Northumberland is most likely to be influenced by altitude and temperature, being at the northern edge of its range in the UK. There remains a paucity of archival and contemporary records for the species and limited recording effort for a species that is very difficult to locate. As a result, there is a real possibility that the species is under-recorded in our region.


Written by Steve Lowe (last updated Nov 12)