Improving the future for two tree-dwelling bat species

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BATS Research and Training Services has recently secured funding to undertake a five-year research project focused on improving the future for two tree-dwelling bat species. The project, which focuses primarily on Bechstein’s and barbastelle bats, has been funded the People’s Trust for Endangered Species and the Arboricultural Association.

The two main aims of the project are:

  1. To improve existing survey methods for identifying bat roosts in trees; and
  2. Learn how to create roost sites by deliberately wounding trees.
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The need

Efficacy of surveys

Surveying trees for bats is challenging. Research of tree-dwelling bat species, such as Bechstein’s and barbastelle bat, highlight the frequent roost switching behaviour. Field signs, such as droppings and smell, only persist for a short period in trees when compared to field signs in buildings. This presents a challenge when trying to protect tree roosts.

A pilot survey, conducted by Jim, has delivered impressive results when using wildlife trail cameras to aid survey of roost sites. This has potential to offer a cost effective and robust solution to this problem. However, further refinement is required before this approach can be rolled out.

Inspecting a Potential Roost Feature
Inspecting a Potential Roost Feature

Loss of roosting habitats

Even where roosts can be identified, the intrinsic dynamic nature of tree roosts means that they will not remain viable forever. Trees fall over, features get damaged, conditions change due to continued decay, etc.

We must ensure that sufficient natural roosting opportunities are available if these species are to survive in the long term. However, our landscapes are becoming more hostile and fewer trees are allowed to develop suitable features.

Whilst some species have been shown to adopt bat boxes, studies have illustrated that these offer sub-optimal conditions due to fluctuating temperature and altered humidity regimes. This is likely to reduce resilience in a population and may in turn reduce the breeding success or likelihood of surviving overwinter. Understanding how to create new roosts in trees is essential to the conservation of tree-dwelling bat species.

Method

Identifying tree roosts

The project will identify tree roosts used by barbastelle and bechstein’s bat by catching and radio tracking individuals. The radio tracking will focus on identifying roost sites of these species.

Locating a roost
Locating a roost

Surveillance of tree roosts

Trail cameras will be mounted outside of the tree roosts to investigate their efficacy. Key variables, such as distance from feature, angles relative to feature, whether the camera records a picture or a video will be tested and the most effective ones identified.

Improving the future for two tree-dwelling bat species - a trail camera setup
Trail camera setup

Roost creation

New roosts features will be created based on the species’ roosting requirements according to the Bat Tree Habitat Key. New features will either be ‘instant’ and ‘future’ features.

Instant features will involve a modification of the nest box design used in a current European Life project led by Vikki Bengtsson of Pro Natura (Sweden). This will involve removing a section of timber from the centre of the tree using a chainsaw, removing the back, creating an access hole and replacing this piece in the tree. Trail cameras will be used to investigate usage of these features. Any evidence of bats (bats, droppings, parasites) will also be documented.

Future features will be created by excavating the desired void size using a chainsaw. Unlike ‘instant’ features, which involve replacing a dead piece of wood back into the tree to close the cavity, future features will be left open at the time of creation. This study will investigate the development of the woundwood growth of the tree and how long it takes to close and offer suitable conditions for roosting bats.

Improving the future for two tree-dwelling bat species - a new roost feature
New roost feature

Timescales

We hope to start this work in 2020, with radio tracking undertaken in August. The new tree roosts will be created this winter (2020/21). From 2021 onwards we will be set up the trail camera experiment, which will run until 2025.

For more information please email [email protected]

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