USE OF BRIDGES AS NIGHT ROOSTS BY BATS IN THE OREGON COAST RANGE

Abstract

We surveyed 10 bridges hourly 1 night/month, April–September 1996, and another 50 bridges on 2 occasions on each of 2 nights, July–September 1996, to assess nocturnal use of bridges by bats in the central Oregon Coast Range. We also collected guano monthly from 28 bridges, April 1996–November 1997, to evaluate temporal patterns of use. Eight species of bats were observed using bridges as night roosts. Bats roosted under cast-in-place concrete bridges in larger concentrations than under other types of bridges and roosted more frequently in end chambers than in center chambers of concrete cast-in-place bridges. Greatest use occurred between 0300 and 0430 h and in June–September, although some bridges were used year-round. We observed females of all reproductive stages, males, and volant juveniles night-roosting under bridges. Our data suggest that size and thermal characteristics of bridges influence use of bridges as night roosts. Further research on use of night roosts by bats would be valuable to more fully understand the ecology of bats.