DALS WILDLIFE SITE { WILDLIFE OF NORTHERN ENGLAND}

WILDLIFE OF NORTHERN ENGLAND

Mammal status UK. Part two Hazel dormouse. Text courtesy of Natural England.org

Hazel or common dormouse. Image courtesy of gbohne {Berlin} CC BY-SA 2.0  license

Hazel dormouse, Muscardinus avellanarius  Habitat preference

The hazel dormouse is found primarily in broadleaved woodland. It is traditionally associated with early successional stages of woodland, as well as coppice, which is structurally similar  (Bright et al., 2006; Juskaitis and Büchner, 2013), but recent studies have shown that it occurs in a range of wooded habitats including scrub, coniferous plantations and hedges (Chanin and Woods, 2003). Rather than being a strict habitat specialist, the hazel dormouse is therefore now seen as more adaptable (Juskaitis and Büchner, 2013). Similarly, although early studies in species-rich habitats showed that the species exploits a wide range of high quality plant foods (flowers, buds, seeds and fruits), it is now known also to occupy habitats with low food species diversity. An omnivorous diet, including significant quantities of insects, may permit this flexibility (Juskaitis and Büchner, 2013).

Status, native. 

Conservation status

• IUCN Red List (GB: VU; England: [VU]; Scotland: n/a; Wales: [VU]; Global: LC). • National Conservation Status (Article 17 overall assessment 2013. UK: Bad; England: Bad; Scotland: n/a; Wales: Bad).

Hazel dormouse in nest Found in a bird box.

Image courtesy of Zoe Helene Kindermann CC BY-SA 4.0 license.

Results

Seventeen relevant papers were returned from the literature search, with four containing prebreeding population density estimates. The remaining papers contained details of the species’ presence, assessments of survey methods, or relative measures of population density. One paper (Bright and Morris, 2005) contained pre-breeding estimates from expert opinion that were included in another source (Bright et al., 2006.

 Median density estimates for hazel dormice with 95% confidence intervals, calculated using data obtained from a review of the literature from 1995 to 2015. Hedgerow length and density within hedgerows are presented as km and km-1, respectively.

 Areas of suitable  habitat and population size 

 England 764,000 757,000 298,000 2,110,000

 Scotland 0 0 0 0

 Wales 200,000 172,000 90,700 529,000

 Britain 964,000 930,000 389,000 2,640,000

734,000 3.0 1.0 8.2 Bright et al. (2006) †† 
Chanin and Gubert (2011) 
Trout et al. (2012) 

Distribution/UK.

Wales and southern England are the strongholds for this species. There is currently only one known population in Cumbria: the area presented in the distribution map may, therefore, be an overestimate. Owing to the levels of interest in dormice, and recording schemes such as the Great Nut Hunt (1993, 2001 and 2009-11) and the National Dormouse Monitoring Programme (Wembridge et al., 2016a), the gaps shown in the species’ distribution in Wales may represent true gaps.

 Percentage occupancy was available from two papers (Bright et al., 1994; Bright et al., 1996), and was based on the percentage of sites surveyed that contained signs of dormice (i.e., gnawed nuts). In Bright and Morris (1996), participants were asked to search hazel

 scrub for signs of dormice, but were not given prior knowledge of sites which were likely to contain dormice. Survey effort, and the availability of hazel nuts, were not standardised, potentially leading to some false-negative results. In Bright et al. (1994), woodlands stratified by age, area and isolation were selected at random, but surveys were conducted only where hazel scrub was heavily fruiting to maximise the probability of detecting dormice, and reduce the risk of false negatives. Survey effort was standardised between sites. The percentage occupancy used in this review was therefore derived from Bright et al. (1994), because more of the potential biases were addressed. Percentage occupancy for hedgerows was taken from Bright and MacPherson (2002), where occupancy was measured from hedgerows in 50 sites. The population estimates for hedgerows, also derived from Bright and MacPherson (2002), were converted into densities (per hectare) using the length and width of hedgerows. As the current analysis considers hedgerows as a linear habitat, these areas were converted to the number of hazel dormice per km, assuming each kilometre of hedgerow had an average width of 3m.

 

Report on hazel dormouse population size 2007-2012 (Joint Nature Conservation Committee, 2013

 England 37,500 minium  37,500 maximum.

 Scotland 0 0

 Wales 7,500 minimum 7,500 maximum.

 Britain 45,000 minimum 45,000 maximum.

 Most of the population is found in broadleaved woodlands (83%), and this accounts for 76% of the species’ distribution (Figure 7.4b). The population density estimate for broadleaved woodland ranged from 1ha-1 to 8.2ha-1, based on nine density estimates reported in three papers. Experts in the field provided population density estimates which broadly agree with those found in the literature, with best-guess density estimates ranging from 1ha-1 to 10ha-1 for broadleaved woodland, and 0km-1 to 28km-1 for hedgerows.

 Percentage occupancy values were estimated from surveys of woodlands containing hazel only. The possibility of dormice living in a wider range of habitats (including those where hazel was absent) was not considered. As recent research suggests that hazel dormice are not specialised to hazel coppice, and are much more adaptable to other habitat types (Juskaitis and Büchner, 2013), the percentage occupancy value of 34% may not be representative of all habitats, and could be a significant underestimate (Paul Chanin, pers. comm.). Conversely, permanent populations are unlikely to be found in woodlands < 20ha, even though these form a significant proportion of woodlands in the species’ range (Tony Mitchell-Jones, pers. comm.); therefore, occupancy may be lower than 34% in some regions

 

 

Future 

Population trend==declining.

Range== stable.

Habitat in decline. 

Changes through time.

Population estimates from Harris et al. (1995) were limited to ancient woodlands, and were reported as 500,000 in Britain, 465,000 in England and 35,000 in Wales. The principal difference between the current review and Harris et al. (1995) is that the latter used a higher estimate of density but a narrower range of habitats. A population density of 5ha-1 was applied to ancient woodlands based on expert adjustment of the density of 8-10ha-1 found in prime habitat. The current analysis includes all broadleaved woodland, rather than ancient woodland only, as well as hedgerows and coniferous woodland. 50% of available habitat was assumed by Harris et al. (1995) to be occupied, as opposed to 34% in the current analysis.

 The National Dormouse Monitoring Programme (NDMP) has assessed trends in relative population size through counts of nest box occupancy in selected sites since 1993. During this period, there has been a steady decline in relative occurrence (numbers of adult dormice found in boxes), particularly in eastern areas, with a 48% (95%CI = 39%-55%) overall decline reported for the 10 years from 2005 to 2015 (Goodwin et al., 2017). Inferences about changes to population size depend on the relationship between nest box occupancy and true dormouse density; this relationship is currently unknown, and may vary over time if alternative nesting opportunities change. A genetic assessment of two British woodlands also revealed that a high proportion of the population was not encountered during nest box monitoring (Naim et al., 2011). Nevertheless, the trends in the NDMP appear consistent between shorter- and longer-term survey periods, and are robust to different levels of survey effort, suggesting that the NDMP currently provides the best available evidence on dormouse population trends (Goodwin et al., 2017).

 

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