Individual study: Managing competition between birds and bats for roost boxes in small woodlands, north-east England
Meddings A., Taylor S., Batty L., Knowles M. & Latham D. (2011) Managing competition between birds and bats for roost boxes in small woodlands, north-east England. Conservation Evidence, 8, 74-80
A total of 196 bat boxes were installed between 2005 and 2009 across 21 sites throughout the Highways Agency's (HA) 'soft estate' woodland in north-east England in support of the HA's Biodiversity Action Plan. The woodlands are typically small linear blocks (<3 ha) with trees mostly less than 40 years of age. Suitable natural cavity sites are thus very limited, hence the attractiveness of bat boxes as a conservation measure to enhance these woodland habitats. Monitoring in 2006-2007 had shown that in some areas (seven woodland sites) over 40% of bat boxes were being used by nesting passerine birds. Bird boxes were installed in an attempt to reduce bird occupancy of bat boxes. Provision of bird boxes significantly reduced bird use of bat boxes (a 50% overall reduction in occupancy) thus potentially making more bat boxes available for bat use. We also assessed if there was any relationship between the number/density of available bat boxes and level of bat occupancy to assess if there was a limit to the occupancy levels that could be achieved, thus determining an approach that could maximise benefits and cost effectiveness of box installation. Occupancy of bat boxes by bats appears not to increase above 30% utilisation with an increasing number of boxes on site after eight boxes. This suggests that, as bat boxes are installed three boxes per tree (as per best practice guidelines), the optimal number to install would generally be between nine to 12 boxes in these small woodland areas.