A colony of rare barbastelle bats, living in the woodlands of the Bovey Valley, has been studied over recent years by researchers from the University of Bristol. Now their detailed work has been published, we can fly through its many paragraphs, results and recommendations to glean an understanding of how woodland bat species make best use of feeding and roosting opportunities among the ancient oak woods.
The shelter and protection offered to this ‘near threatened’ species (see IUCN Red List) from the roosts available throughout the woods are critical to their survival, and the research has provided some useful information to support the ongoing conservation of these fascinating woodland residents. Historically, the woods have been worked by people who have grown crops, grazed livestock, produced charcoal and planted timber trees and the remaining fragments of least-disturbed ancient oak wood have been shown to be the ideal home for the barbastelle. Not only do the bats favour oak trees over any other, the radio tracking work showed how they also preferred standing dead wood as a roost site. The older – the better!
An important factor in their roost choice is the proximity of other roosting features. Rot holes, cracks, splits and tear-out features all provide the bats with a selection of tree cavities that may fit their needs for a variety of reasons. The barbastelle needs this range of roosts so it can, from time to time, switch from one to another to avoid parasites, reduce the risk of predation and maintain social cohesion. These same sites are also used for a long period; in one case, an individual from a roost in 2007 was found in the exact same place some eight years later. The report summarises that, “Radio tracked bats expressed high fidelity to home wood areas and only rarely roosted in other woodland sites.”
Though other woodlands around Dartmoor were used by the researchers, the Bovey Valley Woods of Houndtor and the adjacent area at Becky Falls proved to be among the most common roosting sites. The map shows how the roosts are generally distributed in the ancient semi-natural woodland with a few others located in remnants of ancient oaks within the plantation and scrubby woodlands.
The report concludes that, “Old growth woodland is vitally important to barbastelles and other tree-roosting bats and the preservation and restoration of these habitats should be a conservation priority. Intervention that removes maturing and standing dead trees is expected to signiﬁcantly reduce the carrying capacity of a wood for cavity roosting bats and should be avoided wherever possible.” Dave Rickwood of the Woodland Trust was delighted with the research and was keen to stress that, “These gnarled old oak trees may previously have been felled during forestry operations to ‘tidy up’ the woods, but this research clearly demonstrates their habitat value. In the future, these forked, bent, damaged and dying trees will be left in place.” To enhance the valley’s woods as a barbastelle habitat, the report also recommends that additional tree cavities are created, and an open and diverse canopy structure should be encouraged with a vibrant shrub layer; these features are also likely to provide a healthy habitat for many woodland species beside the barbastelle.
by Matt Parkins
The research was part-funded by the Heritage Lottery Fund through the Moor than meets the eye Landscape Partnership incorporating Natural England, the Woodland Trust and Dartmoor National Park Authority
The full research paper, “Ground-based and LiDAR-derived measurements reveal scale-dependent selection of roost characteristics by the rare tree-dwelling bat Barbastella barbastellus” has been published by Elsevier in the “Forest Ecology and Management” journal.