LOCATING A BARBASTELLE BAT COLONY IN WORCESTERSHIRE
By Johnny Birks
The Vincent Wildlife Trust. firstname.lastname@example.org
Like other so-called ‘tree bats’ that rarely roost in buildings, the barbastelle (Barbastella barbastellus) is probably under-recorded in Worcestershire and in Britain generally. This distinctive, dark-furred species has been recorded widely but sparsely across Wales and southern England, but no breeding colonies were known until 1996/97 when roosts were located in North Norfolk and West Sussex. Recent Worcestershire records date back to the early 1980s when bird ringers accidentally netted a barbastelle at Witley Court. Other 1980s records include one recovered dead by the Rev. Edward Cox at Little Malvern Priory, and I saw one roosting in a mill near Bredon Hill (working for the NCC at the time, I had to stand on a land agent’s shoulders to confirm the bat’s identity!). In 1991 a female barbastelle was recovered from a house in Evesham and cared for by the Worcestershire Bat Group until it was fit for release some two weeks later.
The last five years have seen a welcome growth in our understanding of barbastelles in Britain, largely thanks to new technologies and Frank Greenaway’s detailed study of the West Sussex colony (Greenaway, 2001). In particular, time-expansion bat detectors linked to a recording device (eg. tape or minidisc) now enable bat workers to store and analyse echolocation calls recorded in the field. Sonograms produced by barbastelles are distinctive, showing a short ‘blob’ of sound peaking around 33khz. Using this technology one can visit potential barbastelle woodlands to record bat sounds after dusk, then identify sonograms later on a computer indoors. Although recording effort has increased it is clear that barbastelles remain rare, probably because the types of woodland suitable to support breeding colonies are themselves rather scarce. Recent studies suggest that barbastelle colonies require relatively humid woodland (this condition is often maintained by a dense understorey) containing many old, damaged trees with an abundance of cavities, cracks and crevices available as roosting sites.
Despite a scatter of individual records, no breeding colonies of barbastelles were known in the Midlands before 2003, nor in most of Wales (one colony was found in Pembrokeshire post-2000). In an attempt to improve this situation I joined colleagues at The Vincent Wildlife Trust in a small study using bat detectors to find more sites occupied by the species. We targeted larger woodlands near where each of us lived for individual bouts of detector work after dusk through the summer of 2003. My search area was centred on the Malvern Hills and I recorded my first definite barbastelle on the Herefordshire side on 17th June and another singleton beside a wood near Mathon later in the summer. These encounters with single barbastelles are useful in that they confirm the presence of the species in a locality, but we were aiming to find nursery colonies. On 9th July I recorded eight barbastelles passing me on the edge of a Worcestershire woodland near Little Malvern (close to the Priory where a barbastelle had been found some 15 years earlier). This number of ‘passes’ was exciting because it hinted strongly at the existence of a colony nearby - the first recorded for the Midlands. Elsewhere colleagues found similar evidence of two more colonies in Herefordshire.
Having contacted the Little Malvern woodland owners I returned on several nights through July, August and September, recording many barbastelles within the woodland on each occasion. In particular the high level of barbastelle activity recorded early in the evening within the wood confirmed that it must support a breeding colony. We have identified a couple of ‘hotspots’ where activity is concentrated, but we are still a long way from knowing which tree or trees are occupied by the nursery colony. We have plans for further work in the wood next summer aimed at improving our knowledge of this important colony and its requirements.
GREENAWAY, F. (2001). The Barbastelle in Britain. British Wildlife 12 (5) 327-334.
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