BAT COMMUNITY STRUCTURE IN AN URBAN PARK

In summer 1990, we mist-netted bats on 35 net-nights, for 4 h each night, along tributaries of the River Rouge in surburban Detroit, Michigan, USA. The floodplains of these rivers are preserved as parkland. We compared elements of bat community structure in these urbanized park areas to that of rural areas. For the rural data set, we used mist-netting data obtained previously on 53 net-nights in southern Michigan using a similar protocol. Mean number of bats captured per night was lower in urban compared to rural areas (1.3 vs 4.6). Species diversity (Simpson Index) was lower in the city (0.53 vs 0.28) as was species evenness (0.66 vs 0.36). The big brown bat Eptesicus fuscus made up 65% of the catch in rural areas but 83% in the city. The red bat Lasirus borealis represented 18% of all bats in rural areas and 13% in the city. The proportion of sites where the big brown bat was captured was significantly lower in the city (51% vs 74%). The proportion of sites that yielded red bats also declined, from 52% along rural rivers to only 14% in the city. Sex ratio of adult big brown bats did not differ between urban (43% male) and rural (32% male) sites. The ratio of juvenile big brown bats to adult females was significantly lower in the city (1:21 vs 30:77). Our data suggest that urbanization is a threat to insectivorous bat communities and leads to decreased overall abundance, decreased species diversity, and possibly lower reproductive success of those that are present.