Sharing Expertise on Woodland Bats

During a long mid-summer day, with the woodland canopy glowing green in the sunshine, it was a perfect day for a walk in the woods at East Dartmoor National Nature Reserve, but this time, it was a walk with a difference. Conservation experts from around the SW had been brought together by the Woodland Trust to share the knowledge built up through recent research about a colony of barbastelles, a rare woodland bat species. Over recent years, this colony has been studied by a team from the University of Bristol and a lot has been learned from this work about the way the bats make use of the woodland and surrounding landscape. As the researchers have become better informed about the barbastelles and have begun to draw some conclusions about their roosting and foraging behaviour, the time had come to share this new-found insight. The aim of the day was to transfer the latest scientific understanding to those actively involved in woodland management and the conservation of bat species.

The day began at the Woodland Centre in Yarner Wood where Dave Rickwood of the Woodland Trust introduced the various experts, researchers, woodland managers and habitat conservation advisers. Moving over to Andy Carr from the University of Bristol, the discussion followed a map along the wooded valley of the River Bovey and the Becka Brook. Andy described the various woodland habitats, the locations of the main roosting sites and how the bats had been tracked while moving between those roosts and foraging sites. A number of locations along the valley had been selected for the group to visit during the course of the day and these different habitats would help to put the discussions into context; relevant to the particular features and issues in that area.

Protected Species

The group assembled at the first point along the route where larch timber had been extracted in small volumes over the last few felling seasons. The purpose of this work is to gradually restore the woodland back to a predominantly broadleaved habitat. Dave Rickwood led this part of the discussion, explaining the complexities of managing this type of work, saying “though the larch trees haven’t yet been infected with phytophthora ramorum, we know it could only be a matter of time before we are issued with a Statutory Plant Health Notice. We are trying to extract this timber at the same time as protecting the European Protected Species”.

The discussion continued, looking at how to prioritise the protected species of bats, otters and dormice within the wood, while creating the best habitat for the lower plants that give the valley the Site of Special Scientific Interest status. Finding the ideal time and method for tree work is a difficult task, bearing in mind that the bats may use the ivy on the trees as a temporary roost, dormice may also be active in the area and the timber extraction route crosses the river, a known otter habitat. Though these considerations may provide only a short working window, following best practice makes it possible to prioritise ecologically sensitive woodland management operations.

Bat roosts

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As the group walked through the Bovey Valley Woods, Andy Carr was able to point out some of the individual trees that had been used as bat roosts and point out some of their particular features, for example looking at an oak that was known to have been used by individual male barbastelles, “it was the split in the dead stem of this oak that provided the roosting site”. Near the riverside the group looked at an ancient oak, with its decay holes, splits and cracks the group discussed the value of these veterans of the woods for wildlife.  Dave said that “forestry practice is changing to make sure these veteran trees are left standing. It is now widely recognised that they shouldn’t be tidied up as they used to be because they have the potential to be used by bats and other species”.

Discussions continued to develop and the subject of future research, showed that there is a lot more that we need to know, before the life of the barbastelle is fully understood. With the aim of finding out how roost trees are selected, Andy’s team will be producing a heat map of the valley, to see if temperature has an influence on the location of preferred roosts. Further work is also going on to identify the specific kinds of features on an oak tree that barbastelles favour.  Researchers are using LiDAR results to look at the form or ruggedness of the canopy of an oak wood and how that affects the foraging behaviour of woodland bats.

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Dr Ruth Angell described how her work with sound recorders was providing useful results to show the patterns of foraging flights of various bat species within the woods.

Coniferous woodland

Further along the valley the group stopped to look at an area of plantation conifer woodland. “This area of predominantly Douglas fir is being managed in a commercial style. The timber has a good value so we are working the sensitive wildlife areas first”, explained Dave Rickwood, the site manager. “There is an old oak by the river here that has previously been used by the barbastelles as a maternity roost”. Andy Carr continued to explain how “the peak habitation of this tree was 23 bats, that were counted at one time. It’s a really important roost tree, though it’s not always used by the colony, it is sometimes just used by individual bats”. Dave pointed out that “this is one of those trees that, in the past, could easily have been lost during felling operations but, now we know the conservation value of them, we can prevent them from being felled. Even if oak trees are unintentionally damaged during forestry work, the resulting cracks or decay holes may develop into roosting sites, so these old trees are left where they are”.

As lunch time approached, the discussions were in full swing and the group gathered round a laptop screen to look at some short films that had been made by local volunteer Susan Young. She showed footage from her CCTV cameras of bats entering and leaving a roost. With simultaneous sound recordings, it appears that barbastelles use distinct calls while performing each manoeuvre. She has also filmed a tawny owl attempting to predate bats at their roost. Perhaps this is one of the reasons why barbastelles change roost sites frequently!

The session went on into the afternoon and, though only a short distance had been covered through the woods, the discussion had gone a long way to sharing information about the barbastelle in oak woodland. In the longer term, discussions like this will help researchers, woodland managers and conservationists transfer their knowledge to landscape advisers and land owners on how to better protect some of the rare species most under threat.

This networking event at East Dartmoor National Nature Reserve was organised by the Woodland Trust and Natural England; partners in the Moor than meets the eye scheme, funded by the Heritage Lottery Fund.

by Matt Parkins. With photos by Paul Moody and video footage by Susan Young

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