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CAN HAZEL DORMOUSE HABITAT BE QUANTIFIED BY NESTING BEHAVIOUR? THE INFLUENCE OF VEGETATION DIVERSITY AND STRUCTURE HAMISH JACKSON Introduction The UK population of hazel dormice (Muscardinus avellanarius) is estimated to have declined by 72% over 22 years from 1993–2014 (Goodwin et al. 2017) and this decline is ongoing. The reasons for this are poorly understood, but are likely due to anthropogenic fragmentation of habitat and changes in climatic conditions. Dormice are considered vulnerable to fragmentation because the species is primarily arboreal and does not travel large distances across open ground (Bright 1998). Therefore, extreme cases of fragmentation are likely to cause local extinctions when populations become too small to be viable (Morris 2004). Milder and less predictable winters in Britain are also considered to cause the species to awaken prematurely from hibernation. This would cause a dormouse’s energy reserves to be consumed quicker and would result in a higher potential a higher mortality rate (Juškaitis 2008). As dormice are rapidly declining it is important to examine their habitat requirements to apply effective conservation strategies. Dense vegetation structure and complex plant diversity have been cited as critical elements in defining dormouse habitat suitability (Combe et al. 2016). It is also considered that specific plant species are especially important for dormice populations. In particular, bramble (Rubus fruticosus agg.) and hazel (Corylus avellana) are perceived as important long-lasting food sources, essential for gaining body weight for hibernation in the autumn (Morris 2004; Juškaitis 2007). Oak (Quercus robur) is also considered a valuable food source for dormice as it provides an abundant source of insects during the spring and summer. However, none of these species are essential for viable populations as the species can adapt to survive in a range of habitat types (Juškaitis & Büchner 2013). This investigation was undertaken to determine whether dormice presence is influenced by different vegetation composition, individual plant species and vegetation structure in the East of England. Method The investigation took place in Suffolk and the north of Essex. Sixteen sites were examined, representing a variety of woodland, scrub and hedgerow habitats. Surveys for dormice evidence were undertaken at monthly intervals between March and November 2016 by the Essex and Suffolk Dormouse Group, using nest tubes as a recording method (Plate 10). At each site 50 tubes were placed in woody vegetation along a transect at 15–20 metres spacing. Overall, 800 nest tubes were examined and at each nest tube location vegetation sampling within a nested quadrat of 5m 2 and 10m2 was undertaken. Within the quadrat, a count of all the woody species was provided as well as the estimated percentage cover of each woody species using a Braun-Blanquet scale. Structure was examined by assessing the canopy height, understory density, bramble height and canopy cover at each location.
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The vegetation assemblage of sites was compared by Multi-Dimensional Scaling and PERMANOVA analysis to perceive whether sites with higher nest abundance had similar compositions. A one sample t-test was used to compare whether there was any significance in individual plant species in the quadrats occupied by dormice. Structure was examined by comparing whether quadrats with dormice nest presence had different structural features compared to ones with no dormice presence. Results A total of 174 dormouse nests were found across 13 sites. At two of the three negative sites, dormice were known to be present from previous surveys, but were not detected during this study. It was found that vegetation assemblages were highly variable and unrelated to dormouse abundance (Fig. 1). The 5m2 vegetation assemblage did show that that Kiln Meadow and Mascalls farm had similar vegetation composition, (PERMANOVA, Pseudo-F=1.37, P=0.08), but this was considered unrelated to dormouse nest presence and a similarity was also not found in the 10m2 quadrat. Comparison of dormouse nests to structure also found no significant difference. However, the correlation of individual plant species to dormouse presence found that dog rose (Rosa canina), blackthorn (Prunus spinosa), field maple (Acer campestre), dogwood (Cornus sanguinea) and bramble were significantly linked to dormouse nesting localities. Dog rose had the strongest relationship (p ≤ 0.001), Field maple the second (p ≤ 0.01) and the remaining plant species were all significant (p ≤ 0.05).
Figure 1. Multi-dimensional scaling ordination showing dissimilarity of vegetation composition of sites for Braun-Blanquet quadrat cover-abundance estimates within the 5m2 quadrat.
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Discussion This study has found that it is not possible to quantify hazel dormouse habitat using their nesting behaviour. Dormice nests were recorded in habitats with varied plant assemblages within a range of habitat types and differing ages, which highlights that dormice are an adaptable species. Although dormice were found to preferentially nest close to five woody plant species, it is difficult to assess the benefits of closer nesting to these species other than predicting this relates to food accessibility. With the exception of dogwood, all of these species are known food sources for dormice (JuĹĄkaitis & BĂźchner 2013). However, this shrub produces succulent berries in the autumn and the pollen and nectar of the flowers may produce a spring food source. Consequently, the importance of dogwood to dormice may have been overlooked. Natural dormouse nests have also been found in all of the above species apart from field maple (A. Looser pers. comm. 2017). Dormice are known to make several nests during the active season (G. Verbeylen pers. comm. 2017), so the location of a nest in a tube may be indicative of a group of nests in that locality. It was surprising that hazel and oak were also not significant, as they are described as important, although not essential, plant species in previous research (Bright et al. 2006). Further research should be undertaken on the benefits of dog rose, especially as previous radio-tracking studies found that dormice spend a disproportionate amount of time within the species compared with its availability in the habitat (Bright & MacPherson 2002). This study could not be considered to fully investigate dormouse association to woody species because the survey method only measured dormouse nesting presence within the lower understory. Consequently, the full range of nesting habitat is not taken into account, which is particularly relevant in the summer period where dormice are predominantly active in the canopy (Morris 2004). A further constraint to this study is that dormice move further in a night than the 10m2 quadrats. Two radiotracking studies showed that adult dormice moved mean distances of 156 metres and 143 metres per night. With home ranges of male and females of approximately 0.57 hectares and 0.21 hectares, respectively (Bright & Morris 1991, 1992), this highlights that dormice will likely travel many metres to reach desired plant species, which places less emphasis on the importance of specific woody plants close to their nesting sites. Nevertheless, further studies should be undertaken to examine the value of the woody species which were more frequently present within 10m2 quadrats of occupied nest tubes. Acknowledgements The author would like to thank the Essex and Suffolk Dormouse Group volunteers who assisted by providing the data for dormouse nesting locations. He would also like to thank Dr Paul Ramsay at The University of Plymouth for his mentorship over the course of this project.
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References Bright, P. & Morris, P. (1991). Ranging and nesting behaviour of the dormouse, Muscardinus avellanarius, in diverse low-growing woodland. Journal of Zoology 224: 177–190. Bright, P. & Morris, P. (1992). Ranging and nesting behaviour of the dormouse, Muscardinus avellanarius, in coppice-with-standards woodland. Journal of Zoology 226: 589–600. Bright, P. (1998). Behaviour of specialist species in habitat corridors: arboreal dormice avoid corridor gaps. Animal Behaviour 56: 1485–1490. Bright, P. & MacPherson, D. (2002). Hedgerow Management, Dormice and Biodiversity, Research Report 424. English Nature, Peterborough, 33 pp. Bright, P. Morris, P. & Mitchell-Jones, T (2006). The Dormouse Conservation Handbook. 2nd ed. English Nature, Peterborough. Combe, F., Ellis, J., Lloyd, K., Cain, B., Wheater, P. & Harris, E. (2016). After the Ice Age: The Impact of Post-Glacial Dispersal on the Phylogeography of a Small Mammal, Muscardinus avellanarius. Frontiers in Ecology and Evolution 4: 72. Goodwin, C., Hodgson, D., Al-Fulaij, N., Bailey, S. & Mcdonald, R. (2017). Voluntary recording scheme reveals ongoing decline in the United Kingdom hazel dormouse Muscardinus avellanarius population. Mammal Review 47: 183–197. Juškaitis, R. (2007). Feeding by the common dormouse Muscardinus avellanarius: a review. Acta Zoologica Lituanica 17: 151–159. Juškaitis, R. (2008). The Common Dormouse Muscardinus avellanarius: Ecology, Population Structure and Dynamics. Institute of Ecology of Vilnius University Publishers. Vilnius. 163 pp. Juškaitis, R. & Büchner, S. (2013). The Hazel Dormouse Muscardinus avellanarius. NBB English Edition. Vol. 2. Westarp Wissenschaften, Hohenwarsleben. Morris, P. (2004). Dormice. Whittet Books, Stowmarket, UK. Hamish Jackson The Old School, Church Lane, Brantham, Manningtree, Essex, CO11 1QA
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Plate 10: Hamish Jackson installing a Dormouse nest tube (p. 99).
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