Dozing Dormice (Part 2)

In our earlier Dozing Dormouse blog (Part 1) we explored the usual routes to monitoring dormice either through licensed surveying or through signs of presence – from long empty summer nests – to discarded dormouse dinners of gnawed nuts. 

National Nature Reserves (NNRs) were set up to both protect habitats, species and geology and to be outdoor laboratories.  Science and research continue to be a core objective as part of today’s NNR conservation strategy and therefore dormice have been the focus of wider monitoring undertaken on the NNR to reduce data gaps or to inform management.

(Photo: Matt Parkins)

The standardised monitoring though the National Dormice Monitoring Programme (NDMP) focuses on population and ecology during the active period from May to October, and much less is known about dormouse ecology during hibernation. Hibernation is an adaption to see an animal through unfavourable winter conditions when food is scarce.  Dormice hibernation nests are found at ground level and are hard to locate needing specialist, experienced surveyors searching by hand and eye.  Researchers in other parts of Devon have tried, with varying degrees of success, a number of techniques, including the use of sniffer dogs (which was not successful) and radio tracking. Dormouse hibernation nests are very well insulated within the leaf litter and the state of hibernation means signs of life are less obvious. Body temperature is actively reduced to the ambient temperature of the nest and metabolism slowdown, means that heart rate lowers to 6-13 beats a minute with breaks in breathing.  

An empty hibernation nest, well camouflaged in the leaf litter
(Photo: Matt Parkins)

The timing of woodland management, over the winter, falls mostly during the months of hibernation therefore it is an important to understand the impact on dormouse populations and to avoid disturbance. An additional factor that needs consideration, is that although dormice may stay in one location throughout hibernation, it has been found in a Devon study that as many as half the individuals in a population will move nest sites during periods of arousal, sometimes several times.  

Broadleaf species re-establishing in an area of Hisley Wood where larch trees have been felled (Photo: Matt Parkins)

An ongoing case study within the Bovey Valley woodlands lead by Matt Parkins, licensed surveyor for the Woodland Trust, uses both nest boxes and tubes. The objective of this case study, which began in 2015, is related to woodland management, informing the larch felling taking place at Hisley Wood. The Trust is using a customised approach to Continuous Cover Forestry (CCF), a method of conservation woodland management that balances the need to carefully extract the larch timber, while maintaining and enhancing the wildlife value of the site.  Unlike the National Dormice Monitoring Programme schemes, where nest boxes are fixed in permanent positions for long term monitoring data, the boxes and tubes (placed within hazel coppice and scrub under larch canopies) are moved before and after annual felling. This is to gain greater understanding of the location and movements of the dormouse population and to avoid damage to hibernation nests. The dormice appear to be able to move around the site before, during and after felling, with breeding continuing to take place annually and the population appears to have remained stable.

Larch are carefully felled retaining the hazel understorey (Photo: Matt Parkins)

Although the project has not been subjected to the rigours of scientific study, the observations around the strip-felling zone demonstrate that with careful habitat management, including felling early in the autumn during the active season, limiting machinery access and using pre-prepared winching lines, dormice continued to use the site while conifers were being felled in this species-sensitive manner. The study will be valuable in informing management for other sites where similar conditions exist. 

In a study by Chanin & Gubert (2011) into the relative use of boxes and tubes by dormouse, it was found boxes were used preferentially when given a choice. This does not however preclude the use of tubes where dormice favour the habitat. As part of the above study, Matt Parkins placed tubes and boxes along the valley, away from the larch regeneration area, to provide an indication of the areas that dormice favour – to inform future woodland restoration plans.  Tubes installed on a bracken scrub slope were well used by dormice last summer – bracken can be stripped for nest material in the same way honeysuckle bark is used – individual dormice will use what is locally available.  The results of the wider monitoring indicate they may prefer sunnier aspects, away from humid and shady areas.  

Canopy climbing tuition with Plymouth University (Yarner Wood 2017)

There are other data gaps in the monitoring of dormouse due to the logistics of surveying their arboreal habitat, most data is limited to scrub level monitoring. In 2017 the NNR team were given an opportunity to collaborate with Dr Steve and Sarah Burchett from Plymouth University to install some nest tubes in the canopy of some of our long-term woodland monitoring plots.  Although the results were negative it is important to investigate ways to overcome these data gaps. In the Woodland Trust’s case study of Hisley Wood, Matt Parkins notes that although the density of population appears higher in the coppice area, than in the remnants of hazel under the larch, it is thought likely the dormice are using the higher larch canopy where monitoring is not possible. It is interesting to note, that whilst dormice tails help individuals balance whilst climbing in their arboreal habitat, their tails are not prehensile – there is no ability to grasp.

Some dormouse research monitoring is undertaken using baited hair tubes, that collect hairs on an adhesive tape for later analysis under a microscope. This method is time intensive as tubes need to be re-baited and reset fortnightly, it has the advantage of collecting data on the wider small mammal population, using a site without causing disturbance or relying on the tubes being used for more than a fleeting presence.  This methodology was put forward for a university research project at the NNR, but has not been used to date.  

It is often difficult for individuals to gain the necessary skills and experience to become licensed dormouse handlers enabling them to monitor dormice under the NDMP scheme. Through the Woodland Trust case study above, Matt Parkins has given valuable experience and tuition to ten of the Moor than meets the eye Conservation Assistants during the MTMTE EcoSkills project that ran till September 2019 (in addition to other volunteers) as well as an insight into new woodland restoration management techniques that protect the resident dormouse population. Three of them have subsequently gone on to gain enough experience to become licensed, which takes a minimum of 2 years to achieve.

Continuing monitoring and research are required to ensure that the decline in this diminutive but iconic species is reversed. We are very lucky to have active Devon based researchers investigating the many unknowns of dormice ecology, trialling new monitoring methods such as radio tracking and informing conservation management to protect the local and national population.

Thanks to Matt Parkins for information on the larch restoration management study and supporting local training for surveyors.

Written by Linda Corkerton

Books that may be of interest:
Dormice by Pat Morris
Whittet Books Suitable for older children

Mammal detective by  Rob Strachan 
Whittet Books  Suitable for older children

The Hazel Dormouse by  Rimvydas Juškaitis and Sven Büchner
NBB English Edition Westarp Wissenscaften

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