Dormouse Populations Research Articles

Variation in hazel dormouse (Muscardinus avellanarius) presence in hedge and scrub habitats

Abstract Habitat restoration at a landscape scale is key to reversing the loss of biodiversity arising from habitat destruction. In landscapes that are intensively used by people, such as for agriculture, valuable restoration efforts might be applied not just to ‘prime’ habitats that are known to have strong associations with target species, but also to ‘sub‐prime’ habitats that might nevertheless provide sufficient resources to support populations. Hazel dormouse (Muscardinus avellanarius) populations are in chronic decline in the UK. The species is typically associated with broadleaf woodland but restoration of this habitat at scale in agricultural landscapes is difficult. Other habitats used by dormice might, therefore, provide opportunities for restoration. We investigated the use by hazel dormice of hedgerow and scrub habitats in southwest England. From June–November 2022, using footprint‐recording tunnels, we surveyed 38 hedges and 21 scrub patches in the vicinity of 18 sites known to contain established dormouse populations. We found that dormice were frequently present in scrub (9.3 detections per 100 tunnel checks, 95% confidence interval 6.6–12.0) and less frequently in hedges (4.5 detections, 95% CI 3.2–5.8). In scrub patches, dormice were present more frequently as the abundance of dormice in the closest population increased, and less frequently where bracken (Pteridium aquilinum) was dominant. In hedges, dormice were detected more frequently where there was abundant hazel (Corylus avellana) and honeysuckle (Lonicera periclymenum), as frequency of intersections with other hedges increased, and where an earthen bank was not present. Understanding hazel dormouse association with a wide range of habitats, particularly scrub, offers more opportunities for habitat restoration as part of species conservation strategies.

Prevalence and Molecular Analysis of Encephalomyocarditis Virus-2 in the Hazel Dormouse.

The hazel dormouse (Muscardinus avellanarius) population in the UK continues to decline due to habitat loss, despite reintroductions of captive-bred individuals being conducted nationally for over 30years. Disease surveillance of captive-bred and wild dormice is performed to identify novel and existing disease threats which could impact populations. In this study, we firstly investigated cause of death in seven hazel dormice found dead in England, through next-generation sequencing identifying a virus closely related to a wood mouse encephalomyocarditis virus-2 (EMCV-2). Subsequently, lung tissue samples from 35 out of 44 hazel dormice tested positive for EMCV-2 RNA using a reverse transcriptase quantitative polymerase chain reaction (RT-qPCR) and Sanger sequencing methods developed in this study. Formalin-fixed tissues available for nine hazel dormice which tested positive for EMCV-2 RNA were examined microscopically. Three cases showed moderate interstitial pneumonia with minimal to mild lymphoplasmacytic myocarditis, but no evidence of encephalitis. However, the presence of possible alternative causes of death in these cases means that the lesions cannot be definitively attributed to EMCV-2. Here, we report the first detection of EMCV-2 in hazel dormice and conclude that EMCV-2 is likely to be endemic in the hazel dormouse population in England and may be associated with clinical disease.

Influences of Maternal Weight and Geographic Factors on Offspring Traits of the Edible Dormouse in the NE of the Iberian Peninsula.

The main goal of this study was to analyze the reproductive patterns of edible dormouse (Glis glis) populations in the northeast of the Iberian Peninsula using an 18-year period of data obtained from nest boxes collected between 2004 and 2021. The average litter size in Catalonia (Spain) was 5.5 ± 1.60 (range: 2-9, n = 131), with litter sizes between 5 and 7 pups as the more frequent. The overall mean weight in pink, grey and open eyes pups was 4.8 g/pup, 11.7 g/pup and 23.6 g/pup, respectively. No differences in offspring weights between sexes were found in any of the three age groups. Maternal body weight was positively associated with mean pup weight, whereas no correlation between the weight of the mothers and litter size was found. The trade-off between offspring number and size was not detected at birth. Regarding litter size variation across the geographic gradient (and their climatic gradient associated) from the southernmost populations of the Iberian Peninsula located in Catalonia to the Pyrenees region in Andorra, no evidence to suggest that geographic variables affect litter size was found, discarding (1) an investment in larger litters to compensate shorter seasons related to higher altitudes or northern latitudes, and (2) variation in litter size related to weather changes (e.g., temperature and precipitation) along latitudinal and/or altitudinal gradients.

Isolation Time and Craniometric Differences between Edible Dormouse (Glis glis L., Gliridae, Rodentia) Populations Inhabiting the Greater Caucasus and the Hyrcanian Forest in Southern Azerbaijan

Isolation Time and Craniometric Differences between Edible Dormouse (Glis glis L., Gliridae, Rodentia) Populations Inhabiting the Greater Caucasus and the Hyrcanian Forest in Southern Azerbaijan

Harnessing practitioner knowledge to inform the conservation of a protected species, the hazel dormouse Muscardinus avellanarius

Abstract Conservation decisions are typically constrained by the availability of published evidence. Practitioners and non‐academic experts often possess additional knowledge, including about the practical plausibility of conservation actions, which may lead to more effective planning and outcomes. However, practitioner knowledge is rarely considered during formal evidence syntheses. Alongside a formal literature review, we conducted 26 interviews involving 38 conservation professionals to elicit their knowledge of the conservation of a protected and declining species in England, the hazel dormouse Muscardinus avellanarius. Practitioners and non‐academic experts provided additional insights about dormouse ecology and conservation, beyond those synthesized from the published literature, though we found few contradictions between these different information sources. Instead, practitioner knowledge helped to verify, clarify and expand upon evidence from empirical studies. In general, practitioners emphasized that dormice are far more adaptable than traditionally perceived, with thriving populations found in hedgerows, scrub, road verges and railway verges, rather than solely within broadleaf woodlands. Proposed opportunities for restoring dormouse populations included improving hedgerow management, creating new woodlands, bringing existing woodlands back into management, setting aside unproductive land and improving habitat connectivity. However, participants emphasized the need for landscape‐scale approaches, accounting for the impacts of climate change, and better surveying and monitoring. Key practical considerations included overcoming time and financial constraints, providing better advice, knowledge and training, changing attitudes of land owners and managers and balancing other demands such as agricultural productivity and the requirements of other species. Despite the insights they provided, participants highlighted many remaining knowledge gaps. These included uncertainties arising from the published literature, as well as scarcely studied topics that are of major practical importance, namely the effectiveness of dormouse mitigation measures in planning and development, and the impacts of anthropogenic disturbance and pollution on dormice. Our findings improve the evidence base for restoring hazel dormouse populations and for further empirical evidence gathering. More generally, the study highlights how practitioner knowledge can help both to supplement traditional published evidence and to better frame conservation programmes, which may lead to more successful outcomes.

The effect of climate on age specific survival and senescence in a Hazel Dormouse (Muscardinus avellanarius) population in Lithuania, across 1997-2021

It is well known that survival and the dynamics of wild populations are affected by environmental factors. Recent research has found that, among some species of mammal, differences in environmental conditions between populations of the same species translate into changes in infant and juvenile mortality, but not in the rate of senescence (‘rate of aging’). This has been confirmed among primates and some species of carnivores, but has not been tested on other taxonomic groups, such as rodents. Here, we analyse age-specific survival and mortality on the most extensive capture-mark-recapture data set on Hazel Dormouse available from Lithuania. We used Bayesian survival trajectory analysis (BaSTA) and tested different models of age-specific mortality. Since the Hazel Dormouse population is in decline across its northern distribution, potentially in response to climate change, we divided the data into three periods to assess changes in survival over time. Regional climate data were obtained from the NOAA data service to test the effect of climatic factors on survival during winter and summer respectively. Our results show that, during all three periods, male life expectancies were longer than those of females. We found that the overall level of mortality was high for all three periods, with lowest mortality during the period 1999 - 2004. We found large differences in juvenile mortality and age-independent mortality between the three periods, but not in adult mortality or in the rate of senescence. This is consistent with previous findings on other mammals, supporting the invariant rate of aging hypothesis.

Quantification of Edible Dormouse (Glis glis) calling activity for biodiversity surveys: comparison of core and peripheral populations

In Lithuania, the Edible Dormouse (Glis glis) is an endangered red-listed species and only 10 populations are known at present. It is situated on the northern periphery of its distribution range and outside the continuous range of the European Beech (Fagus sylvatica) which is a key-species for this rodent. For this reason, habitats of the Edible Dormouse are completely different in Lithuania, where most dormouse populations are fragmented, isolated and might be very small compared to other countries, where beech stands predominate in Glis habitats. Alhough the Edible Dormouse is a well-investigated species in many parts of its range, there is still a lack of information about the ecology of this species on the periphery of its distribution range. In this presentation, we compare calling activity of the Edible Dormouse in core and peripheral populations using voice recorders. During the summer 2017, three voice recorders were deployed on three permanent sites in the Czech Republic, and three voice recorders were deployed at three different localities in Lithuania during the summer 2020. Voice recorders were continuously recording dormouse voices over the entire summer until the beginning of autumn, and relevant days of voice records were selected for the comparison of calling activity. The results of this study will help to evaluate a new method for Edible Dormouse investigation in Lithuania, revealing new and interesting information about its nocturnal life.

The beginning of the dormouse monitoring program in Normandy, France (Poster presentation)

Bibliography can be used as a source of informations on the ecology and threats to the Hazel Dormouse. However, little data is available on French dormouse populations, and population trends remain unknown. The Hazel Dormouse is a protected species in France, but no particular attention is afforded to it by political policies. In 2018, the GMN (Groupe Mammalogique Normand) started a dormouse monitoring program in Normandy (France), based on volunteer work by its members. The aim of the program is to obtain information about local dormouse populations using nestbox monitoring at 10 study sites spread throughout Normandy, over a period of 5 to 10 years. The first years of the program were devoted to the search for potential study sites, the construction of nearly 400 nestboxes and their installation and monitoring at 8 study sites (beginning in 2019 for the first site). Since then, Hazel Dormouse nests and/or individuals have been observed in nestboxes at 7 study sites, with interannual fluctuations. The GMN is expanding its research to an additional two new sectors in 2022 or 2023. Further analysis will follow over the next few years.

Ticks on the Edible Dormouse (Glis glis)

Rodents in central Europe, such as the Edible Dormouse, are common hosts for many ectoparasites, including ticks. One of the most extensively studied tick species is Ixodes ricinus, whose geographic distribution extends from Scandinavia to Morocco. In 2014, a new North African species I. inopinatus was described and found in Morocco, Tunisia, the Iberian Peninsula, and peripherally also in Romania, Austria, and southern Germany. Both Ixodes species were reported in sympatry in southern Europe (Spain and Portugal) where they feed mainly on lizards. During the period from early June to October in 2016-2019, we captured 4597 dormice and calculated the rate of tick infestation. Our results show that the mean prevalence of ticks in the dormouse population was 31.9 %. In the next step, 400 ticks from 2019 (255 larvae, 144 nymphs, 1 adult) from dormice were identified morphologically and by multiplex-PCR to distinguish I. ricinus and I. inopinatus. The results of our analysis show the first report of I. inopinatus feeding on rodents.

When is a dormouse ‘Endangered’? Continued population decline of Hazel Dormice (Muscardinus avellanarius) in Great Britain. (Poster)

It is important to monitor species populations to identify changes in Red List assessment, whether increases from conservation or continued declines. This can be more difficult when there are multiple modelling options available. Using data from the National Dormouse Monitoring Programme, provided by the People’s Trust for Endangered Species, we explore the change in British Hazel Dormice (Muscardinus avellanarius) populations using two appropriate generalised additive models. The first uses the negative binomial distribution, and second the Poisson distribution, with a fixed effect of month included. Both models indicate that dormice have declined by >70% between 1994 and 2018 in Great Britain, indicating a continuation of the chronic decline of the species. Our models do not differ significantly in their evaluation of the population trend, but do indicate different Red List categories, leading us to ask: when is the dormouse population considered ‘endangered’?

Nest sites used for daytime rest in urban Garden Dormice (Eliomys quercinus) in Wiesbaden, Germany

Garden Dormouse (Eliomys quercinus) populations have declined by 50% throughout Europe over the last 30 years. They are increasingly found in German cities, but little is known about their urban lifestyle. A radiotelemetry study was performed in the city of Wiesbaden, to investigate the daily resting habits of Garden Dormice. The location and structure of nest sites used for daytime rest (DNS) of five individuals (one female, four males) were recorded each to every second day during the months of May to July 2021. The animals were located 90 times in total in a DNS, and two to six different DNS per animal were identified. DNS were found in hedges, trees, bird nests, facade greening, nest boxes, and inside buildings. Garden Dormice in this study were often located in DNS that provide consistent temperatures (false floors, walls) and a high degree of protection from predators. DNS with visual cover and possible food supply (facade greening, hedges) were also often used. The frequency with which DNS were changed varied greatly depending on the individual. The dormice in this study showed adaptations to urban living, as each animal used at least one anthropogenic structure as DNS. Recommended conservation measures for Garden Dormice in urban areas, based on this study, include raising public awareness and protection and promotion of facade greening (climbing plants on walls and fences), hedges and old buildings. Further research on the life of Garden Dormice in urban areas is needed.

Trials of Edible Dormouse (Glis glis) population reduction in a British woodland

In the UK the Edible Dormouse is a non-native pest occurring in c.1000 sq.km of the Chilterns area, west of London, but it is spreading. It causes damage to biota in woodlands and is also increasingly present within buildings. Licenced humane culling (killing) is allowed in the UK and it is illegal to release them if captured alive. Poisoning is illegal. Several thousand are culled in buildings annually. The results of capture trials of adult Glis within our research woodland in 2010, 2019 and in 2020 are reported. From 40 nestboxes, 126 individual dormice were removed over 10 continuous days in July 2010 and released on the nearest adjacent tree (>80% of all adults recorded there in that year). In 2019, 72 catching devices were added to 26 established boxes in a 12ha. semi-isolated triangle of woodland. In 10 days 169 were culled. Five weeks later, 68 were found (not culled), indicating 20/ha overall and a maximum cull of 72%. Since 2019 was a non-breeding year (when many long-lived adults do not appear in our trapping record) we hypothesised that some old Edible Dormice not seen in 2019 might be captured in 2020. In 2020 two 5-day trapping periods were undertaken. In early July 160 were culled and another 110 four weeks later. We captured 36 more adults later; in total representing 26.5/ha. In 2021 monitoring revealed a minimum of 63 adult Glis. The capture data, movements, cost effectiveness and implications for control are discussed.

Was everything better in the good old days? Declining body mass in the Garden Dormouse (Eliomys quercinus)

Garden Dormouse (Eliomys quercinus) populations have shown a drastic decline over the last 20-30 years, the reasons for this decline are still unknown. In wild animals, body mass is a good indicator of fitness and survival probability, especially in hibernating species like dormice. Fat accumulation before the onset of hibernation and juvenile growth are crucial to survive the following winter. We conducted a capture-mark-recapture study in the Black Forest (south-western Germany) between 2018 and 2021 and compared the body mass of captured Garden Dormice with data collected between 2003 and 2005. Furthermore, we investigated the dietary spectrum of this species by faecal analyses. The results show that adult Garden Dormice nowadays have a significantly lower body mass (difference 11 ± 2.8 g) before the onset of hibernation than two decades ago. Furthermore, juveniles showed a significantly lower body mass gain in the years 2018-2021 compared to juveniles in 2003-2005. Dietary analyses have revealed that insects represent the main food resource for juvenile Garden Dormice and also in adults during pre-hibernation fattening. This study shows, that the body mass of the Garden Dormice in the Black Forest has decreased over the last two decades, which could reduce their reproductive success and their survival rate, especially during hibernation. A reason for this body mass reduction could be the severe decline of insects leading to an insufficient availability of the key food resource of this species. In particular, reproductive females might not be able to cover their investment during gestation and lactation.

Alpine forests are a suitable habitat for the Hazel Dormouse

The Hazel Dormouse (Muscardinus avellanarius) is commonly considered a typical lowland species, occasionally observed at higher elevations in mountain habitats. This study began with preliminary investigations in the Gran Paradiso National Park in the Western Alps, where nests of Hazel Dormice were observed at around 2000 m a.s.l. In 2019, a mark-recapture project started in two valleys (Valsavarenche and Val di Rhêmes), positioning six grids with 40 nest boxes from 1000 m to 2000 m a.s.l. to investigate the ecology and adaptations of dormouse populations along the altitudinal gradient. In these years, nest boxes were checked irregularly, and the number of marked animals was low. The number of individuals captured in the highest grids at 2000 m increased from 1 to 8 in Valsavarenche and from 11 to 15 in Val di Rhêmes. These results seem to confirm a continuous presence of the species at the upper edge of the forest vegetation. The data from Valsavarenche suggest some significant population fluctuations, but the effect of nest boxes on population densities cannot be excluded.

Acoustic detection of Garden Dormice: a field mapping study in an urban habitat in Germany

Garden Dormouse populations have been decreasing in range and declining in number throughout Europe. For effective conservation strategies, it is important to know where and in which habitats the species still occurs. Effective monitoring methods are therefore urgently needed especially because Glirids are difficult to monitor due to their nocturnal activity and their relatively low population density. The city of Wiesbaden (central Germany close to the River Rhine) harbors a stable Garden Dormouse population. In summer 2019 a field mapping study was conducted in which the occurrence of this species was investigated. During the summertime detection of the animals, based on their characteristic vocalizations, was used for the first time to map the occurrence of the species. Within 20 nights we obtained 128 acoustic detections of Garden Dormice, involving at least 168 individuals, and resulting in records for 55 out of 61 km² grids investigated. In Wiesbaden, the species is widespread and could be easily detected by its calls. It was found over almost the whole area, mainly in semi-open areas like gardens and allotments, but also in highly built up and cultivated areas, right in the immediate vicinity of humans, and in some cases even inside buildings. Thus, the Garden Dormouse has successfully adjusted to a life in an urban environment. Using this simple, cheap, fast and non-invasive method can provide many data for biodiversity monitoring and should therefore be given more consideration in future surveys.

Comparing methods to detect Garden Dormice (Eliomys quercinus) in mountainous forest habitats

Garden Dormouse populations show a severe and ongoing decline all over Europe. The drivers for this process are still unknown, as well as the exact distribution of the remaining populations. An evaluation of the occupied habitats could give information on important habitat parameters. Therefore, it is essential to improve detection methods and to evaluate the efficiency of available techniques. In this study, three different methods were tested on ten transects in the Fichtel Mountains, Germany. On each transect we installed two camera traps (CT), one autonomous sound recording unit (AudioMoth, AM) and 25 footprint tunnels (FT), which were checked weekly from the beginning of June until the end of October. AMs did not record a single call, FT detected Garden Dormice in seven and CT detected them in all ten transects. FT worked best during July, when they provided evidence of Garden Dormouse on six transects. CT worked best in August and September, confirming Garden Dormice in all ten transects. In every month, CT outperformed FT in the number of positive findings, and in the time interval until initial detection. CT worked most efficiently in this type of habitat, whereas FT produced false absence data. As Garden Dormice inhabit a variety of different habitats, this study should be repeated to see if the results are transferable.

Relationships between climate variables, seed production and reproduction of the Edible Dormouse (Glis glis) in mixed oak forests of the Iberian Peninsula

The Edible Dormouse (Glis glis) is a small arboreal mammal that lives in deciduous forests in much of Europe, the Iberian Peninsula being one of the southern limits of its distribution. Some studies have shown that this species uses the strategy of anticipatory reproduction, which means that it adapts its reproductive effort to seed production, such as beech mast and acorns, which varies greatly from year to year. The Edible Dormouse anticipates future seed availability of the coming autumn and modulates its reproductive effort, as beech mast and acorns are a crucial resource for the young to survive their first hibernation. This work aims to determine the correlations between annual variations in climate and seed production, and their effect on Edible Dormouse reproduction using 9 years of data (2012–2020) in two natural parks in Catalonia (Montseny and Montnegre-Corredor). These are located at the southernmost limit of the distribution of this species in the Iberian Peninsula. The results show that the productivity of Beech trees (Fagus sylvatica) is conditioned by local meteorological conditions and pollen availability, and that the acorn production by oak trees (Quercus sp.) is also affected by local meteorological conditions, but not by pollen availability. Additionally, breeding by the Edible Dormouse in Montseny has shown high synchrony with acorn production and that the presence of beech seeds increases the number of offspring per female. These results encourage us to conduct future studies to predict how Edible Dormouse populations will be impacted by climate change.

Distribution of Glirids in an Alpine national park

In this long-term study, we evaluated the distribution of three species of Glirids: Hazel Dormouse (Muscardinus avellanarius), Garden Dormouse (Eliomys quercinus) and Edible Dormouse (Glis glis) in the Gran Paradiso National Park (Western Italian Alps). The aim was to investigate the ecology, adaptation strategies, and distribution of these dormouse populations along an altitudinal gradient. Monitoring started in 2015 and is still ongoing. We used five different techniques (searching for nests, grids of nest boxes, transects of live traps, nesting tubes, and footprint tunnels), placed along an altitudinal gradient from 700 to 2300 m a.s.l. We found a total of 680 signs of the presence of Hazel Dormouse and 46 individuals, 275 signs and 142 individuals of the Garden Dormouse and 674 signs and 67 individuals of the Edible Dormouse. The three species selected different altitudinal gradients: Edible Dormouse from 800 to 1700 m, with a prevalence between 800-1100 m; Garden Dormouse from 1100 to 2000 m, with a prevalence between 1400-1700 m. The Hazel Dormouse was ubiquitous from 800 to 2032 m, without a clear altitudinal pattern. Edible Dormice were mainly found in deciduous and mixed forests, while Garden Dormice usually occurred in coniferous forests. The Hazel Dormouse seemed to be regularly distributed in all forest types up to the tree limit. These results, obtained from diverse methodologies, permitted comparison between the monitoring protocols, improved knowledge of habitat selection by Glirids in Alpine habitats, as well as providing novel insights within the context of climate change.

Road mortality in Hazel Dormice (Muscardinus avellanarius): first evidences for this species and implications for road mortality research

Roads are considered major movement barriers for the Hazel Dormouse, a strictly arboreal mammal. Recent evidence shows that they inhabit roadside habitats and can safely cross roads, but no evidence of road mortality has been documented so far. In our study we investigate the occurrence of safe road crossings and roadkills using direct observation during optimal activity of Hazel Dormice, by surveying 35 km of national and local roads transects in Romania. The transect crossed a representative landscape with forests, pastures, arable land and small villages. We encountered Hazel Dormice on roads on 21 occasions, out of which 10 were roadkills, 8 were safe crossings and 3 were individuals standing by the side of the road. Our study gives direct evidence that safe crossings do occur, but also documents road mortality in this species for the first time. We explored the habitat context around the roads to understand the determinants of road crossings. We found that woody and shrubby vegetation elements in the vicinity of the roads are important, especially in arable dominated landscapes. Factors influencing road crossing behaviour and the ways mortality impacts the dormouse population are still largely unknown. Understanding these can improve mitigation actions.

The Dormouse Reintroduction Program in the UK

Hazel Dormice have been lost from 17 English Counties over the past 150 years and the population has declined by 51% since the year 2000. The dormouse reintroduction program has been running since 1993 with the aim of restoring dormice to their native range in the UK. In the early years, a single dormouse population was released in a suitable woodland with the hope that it would occupy all available habitats in the release site and then start to disperse into the wider countryside. While this approach did have some successes, it also had some failures. The program was reviewed in 2014 and some amendments were proposed to the original protocol. A key amendment was to identify at least two woodlands at a site, in relatively close proximity, each suitable for a dormouse release and to undertake at least two reintroductions in an area. Further to the dormouse reintroductions, a landscape project would be established to improve connectivity between the woodlands. The longer-term aim is now to facilitate the creation of a dormouse metapopulation in an area rather than just hoping it would happen. This talk discusses the advantages and difficulties of this new approach and its successes and failures.