Bat activity in an urban landscape: Patterns at the landscape and microhabitat scale

Relatively little attention has been devoted to the urban ecology of bats (Chiroptera) despite their ecological importance. Although previous studies,have indicated that urbanization has a negative effect on the abundance of bats and bat activity, this relationship may differ among regions. We monitored bat activity during 1997-1999 in 1520 natural areas distributed across a 3500-km(2) area spanning the Chicago metropolitan area in northeastern Illinois. Our objectives were to elucidate relationships between landscape and microhabitat characteristics and bat activity. Bat activity was correlated with visual estimates of abundance. Among adjacent land-use classes, industrial/commercial use was positively related,to bat activity in 1997 and 1999, and the predominant rural land use, agriculture, was negatively associated with bat activity in 1998. Proportion of woodland habitat within study areas was positively related to bat activity in every year. There was a positive relationship between agricultural land use and relative use of water sites in each year. Microhabitat analyses revealed that distance between trees was positively related to. bat activity in woodlands, and-in open habitats there was a relatively strong, negative relationship between distance from the edge and bat activity. Within open habitats, mowed areas had more bat activity than agricultural areas. Our landscape results suggest that the relationship between urbanization and bats may be related to context. Heterogeneous urban landscapes may represent islands,of habitat for some bats within larger landscapes dominated by intensive agriculture, such as much of the Midwest.