Bat Activity Decreases as Diversity Increases in a Transition from Urban to Rural Habitats: Implications for Urbanisation

Bat activity estimated using bat passes along 12 km of a valley bottom in southern England, UK, confirmed the trend of lower species diversity (H') in urban compared with rural habitats. Pipistrellus pipistrellus accounted for 57.48% of passes (n = 3,532), most of which were recorded in the urban part of the valley, confirming the urban fallout driven by dominance of this species. Where the valley bottom transitioned from urban to rural habitats, species diversity (H') increased. However, overall bat activity decreased, driven by a dramatic decline in the number of passes of P. pipistrellus in rural areas. Conversely, activity of Pipistrellus pygmaeus and five other bat species/species groups, each of which accounted for less than 25% of passes, was higher in rural areas. This transition was interrupted at a small scale (250 m) by ‘hotspots’ of high bat activity associated with favourable habitats (e.g. a mill pond) and ‘coolspots’ (e.g. ground cleared of vegetation prior to housing construction). The results indicate that ongoing building works within the valley would affect the bat assemblage in different ways depending on the surrounding landscape. In rural areas, an increase in the extent of built structures and other hard surfaces could increase overall bat activity but decrease diversity (H’) as scarcer species undergo ‘urban fallout’.