Rafinesque's Big-Eared Bats

ABsrnAcr.-Rafinesque's big-eared bats (Cc1)'llOrhinus mjinesquit) use bridges as day roosts in parts of their range, but information on bridge use across their range is lacking. From May to Aug. 2002 we surveyed 1129 bridges (12.5%) within all 46 counties of South Carolina to determine use and selection of bridges as day roosts by big-eared bats and to document their distribution across the state. During summer 2003, we visited 235 bridges in previously occupied areas of the state to evaluate shm-Herm fidelity to bridge roosts. We found colonies and solitary big-eared bats beneath 38 bridges in 2002 and 54 bridges in 2003. Construction type and size of bridges strongl}' influenced use in both years; bats selected large, concrete girder bridges and ayoided flat-bottomed slab bridges. The majority of occupied bridges (94.7%) were in the Upper mid Lower Coastal Plains, but a few bridges (5.3%) were located in the Piedmont. Rafinesque's big·eared bats were absent beneath bridges in the Blue Ridge l\'fountains. We established new records of occurrence for IO counties. In the Coastal Plains, big-eared bats exhibited a high degree of short-temlHdelity to roosts in highway bIidges. For bridges that were occupied at least once, mean frequency of use was 65,9%. Probability of finding bats under a bridge ranged from 0.46 to 0.73 depending on ",hethelthe bridge was occupied in the previous year. Thus, bridges should be inspected three to fiye times in a given year to determine whether they are being used. Regional bridge roost suryeys may be a good method for determining the distribution of C. rafinesquii, particularly in the Coastal Plains, and protection of suitable bridges may be a viable conservation strategy where natural roost sites are limited.