Factors determining the abundance of vespertilionid bats in Britain: geographical, land class and local habitat relationships.
Transect surveys of foraging bats in a stratified sample of 1030 1-km squares in Britain were used to compare bat abundance in different land classes. Bat abundance remained constant during summer, but varied significantly between land classes. Increased ambient temperatures caused increased local abundance of bats. High abundance occurred within arable and pastoral land class groups in the south, while low abundance occurred in arable, marginal upland and upland land class groups in the north. Regression analysis identified a significant negative gradient in bat abundance on a south-north axis in Britain and also on a west-east gradient within a transect across N. Wales and the English Midlands. Regression analyses further outlined significant relations between bat abundance and habitat availability within 7 land class groups. Habitats included in models were similar for each land class group. In general, bat abundance was positively related to the availability of woodland, vegetation corridors, lacustrine and riverine habitats, and negatively related to the availability of arable land.