Arboreal Bridge Trial for Hazel Dormice
Written By Darrelle Moffat
Connectivity Ecologist, Animex International
16th September, 2020
The Hazel Dormouse (Muscardinus avellanarius) is a nocturnal rodent native to parts of Europe. They are highly arboreal, moving within the tree and shrub canopies and prefer to cross arboreal habitats rather than along the ground. Dormice have particular habitat requirements including dense and diverse tree or shrub cover that allows arboreal movement and provides food throughout the year, dense foliage for weaving breeding nests and suitable locations at ground level for hibernation. In the UK, roadside habitats are important as species-rich, connected woody vegetation.
In the UK, the Hazel Dormouse population is estimated to have declined by half in the last 100 years, with a significant decrease in range. It is legally protected under UK and EU law, also including its breeding sites and resting places. Although the dormouse is protected in the planning process, its population is estimated to still be declining at a rate of 5.8% annually. Extensive urban growth is leading to continued habitat fragmentation, particularly by linear infrastructures such as railway and roads. This infrastructure restricts population movement, meaning dispersement of juvenile dormice, establishments of metapopulations and gene transfer is all reduced.
Dormouse crossings have been constructed previously in the UK to connect habitats. However the only proven dormouse bridge is a large vegetated land bridge, with a substantial cost and limited opportunities. Other smaller designs have also been attempted, such as enclosed mesh tubes or rope bridges but there have never been any dormice recorded using these bridge designs and these often offer only a short-term solution. Many structures also haven’t taken the wider landscape into perspective and have been installed in unsuitable locations.
In Japan, a trial was undertaken to test a new design for the Japanese Dormouse (Glirulus japonicas), which recorded the dormice, and three other mammals, using the structure. The Japanese design inspired the design for trial in the UK. This UK trial was conducted on the Isle of Wight in Southern England, where a bridge approximately 30m in length was used to connect woodland habitat either side of a railway, extending 3m into the habitat on each side. It was erected over an existing railway bridge.
The trial compared the quantity of dormouse events on the bridge against a control of dormice on the ground. Wildlife exclusion fencing was installed either side of the railway, centred on the bridge and extending a total of 200m, reflective of a typical home range for the hazel dormouse. Small holes were made in the fence at 30m intervals and a motion-activated infra-red camera was placed at each of them to record activity (18 total ground cameras). Six cameras were also placed on the bridge at strategic points to capture activity across the entirety of the bridge. The bridge was originally installed September 30, 2015 and in place until October 10. The bridge was then reinstalled in spring and the trial period extended from April to November 2016.
The first dormouse event on the bridge occurred only 9 hours after installation. A total of 39 hazel dormice events were recorded - 36 on the bridge and 3 on the ground, none of which entered the holes to cross. Therefore, the dormice seem to have a preference for using the bridge rather than the ground. The design of the structure likely has contributed to this, providing multiple access points from the sides and movement around different parts of the bridge throughout the entirely of the bridge, and multiple points of shelter to allow them to seek over. The observed individuals appeared at ease on the bridge, possibly due to the opportunites given by the design.
The trial design and materials have now been upgraded to be compliant with highways legislation and to offer a long-term habitat connectivity structure. Since the dormice were recorded on the 30m bridge, approximately the width of a UK dual carriageway, the design could provide connectivity across highways of a similar length.
Author information:
Author: Darrelle Moffat, Connectivity Ecologist, Animex International, Lee on the Solent, Hampshire UK
Email: darrelle@animexbridge.com
Source:
White, I.C. & Hughes, S.A. (2019). ‘ Trial of a bridge for reconnecting fragmented arboreal habitat for hazel dormouse Muscardinus avellanarius at Briddlesford Nature Reserve, Isle of Wight, UK’ Conservation Evidence, 16, 6-11. https://www.conservationevidence.com/individual-study/6953
Editor:
Rodney van der Ree
Cite this summary:
Moffat, D. 2020. Arboreal Bridge Trial for Hazel Dormice. Edited by van der Ree, R. TransportEcology.info, Accessed at: https://transportecology.info/research/dormouse-bridge-trial [Date accessed].