Tuesday, 24 April 2012

Norwich goes batty for bats

From time to time I will see or hear a bat flitting across my urban garden – I can still just about pick up the pitch of their echolocation calls. I definitely have Brown-longed Eared Bats visiting because I see them sometimes, perched on the wall of the passageway that runs under the upper floor of the house. They seem to like this sheltered spot and use it as a place to dismember some of the larger moths that they catch. Come morning, there is often a pile of discarded moth wings on the floor of the passage, and a sprinkling of bat droppings stuck to the rough wall.

Brown Long-eared Bats forage using two different strategies. As well as capturing prey during flight, as is the case in most other bats, they also take prey from vegetation, a behaviour known as foliage gleaning. This underlines an association with well-vegetated habitats – across much of its European range the Brown Long-eared Bat is a woodland or forest species. In Britain, however, there is a strong association with buildings, the species favouring them for its summer roosts, and so it is not unsurprising that they should be found hunting within an urban setting. I suspect that my garden is used because it is a part of a larger block of urban green space, complete with some mature trees and much shrubby cover.

There is much to learn about urban bat communities and this is one reason why Dr Stuart Newson and Norwich Bat Group have launched a new study. Called The Big Norwich Bat Project, the study aims to carry out bat surveys across the whole of the city and its surrounding area. The team are using cutting-edge devices that monitor bat activity throughout the night by recording the echolocation calls of any bat that happens to pass within range. The recordings are then downloaded and analysed by running them through computer programs; these compare the calls heard with a library of calls for which the identity of the species is already known. This approach has already made a significant contribution to our understanding of the distribution of bats elsewhere within the county.

The team aim to deploy a device in each 1-km square within their study area and are still looking to fill some gaps in their coverage. Take a look at their website (www.norwichbatgroup.org.uk/project.html) to see if your garden could be used to plug a gap. If the project proves successful then maybe the approach can be extended to cover other urban areas within the county. I’d certainly like to know what other bat species might happen to be using my garden when I am tucked up in bed asleep.

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