O’SHEA, CRYAN & BOGAN: UNITED STATES BAT SPECIES OF CONCERN 
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573 meters apart (range 120 meters to 4.0 kilometers; Trousdale et al., 2008). In a South Carolina 
study, Rafinesque’s big-eared bats used anthropogenic structures more often than hollow trees in 
summer, but not in other seasons; movements among roosts were related to thermal differences 
among roosts (Loeb and Zamoch, 2011). 
These bats use several different kinds of bridges. Concrete bridges are utilized as diurnal roosts 
in many areas (Lance et al., 2001; Trousdale and Beckett, 2004; Ferrara and Leberg, 2005a,b; Ben¬ 
nett et al., 2008). In Louisiana, these bats utilize bridges with “double-T” understructures (Lance 
et al., 2001, Ferrara and Leberg, 2005a,b). Most of the bats found under these bridges were not in 
colonies but were solitary or roosted in small numbers. These solitary and small groups of 
Rafinesque’s big-eared bats roosted in microhabitats under these bridges that were warmer and 
darker than other areas under the same bridge, but about 5°C cooler than ambient; roosting points 
also tended to be closer to abutments but far from the edges (Ferrara and Leberg, 2005a). Mater¬ 
nity groups of five to 85 bats roosted under concrete bridges in the Kisatchie National Forest in 
Louisiana (Ferrara and Leberg, 2005b). 
Well over 1,000 bridges were surveyed for Rafmesque’s big-eared bats throughout South Car¬ 
olina; diurnal roosts of solitary bats or colonies were found at 73 bridges (Bennett et al., 2008). 
Numbers of bats in colonies fluctuated between repeat visits to bridges within a summer, but 
colony size ranged from two to 53 with medians of eight to 12 bats in two different summers of 
surveys. Bats preferred roosting between support beams rather than in expansion joints, and over 
banks near abutments rather than over water (Bennett et al., 2008). Bats used larger bridges and 
bridges with T-beam or multiple beam girders rather than slab bridges in South Carolina, and most 
(95%) bridges with roosting bats were over rivers in the Upper and Lower Coastal Plains physio¬ 
graphic regions rather than in the Piedmont or mountains (Bennett et al., 2008). Investigators deter¬ 
mined that bridges should be visited three to five times per year to assure detection of use (Bennett 
et al., 2008). 
McDonnell (2001) surveyed 990 bridges and culverts for use by bats in the Coastal Plain of 
North Carolina during summers 1997 and 1998. Rafinesque’s big-eared bats were found roosting 
in 36 of these structures, with 25 of the 36 structures housing solitary bats, several with 2-9 
females, and one with a maternity colony of about 40 bats. All but one structure used by these bats 
were in swamp or bottomland hardwood forest habitats, and only one steel culvert was used, hous¬ 
ing a solitary bat. Rafinesque’s big-eared bats were never found roosting under the 105 concrete 
slab bridges, 87 steel multi-beam bridges, or 65 concrete box culverts investigated (McDonnell, 
2001). These bats were found most often under I-beam bridges, followed by channel beam bridges, 
T-beam bridges, and timber multi-beam bridges. Bridge use was related to degree of disturbance 
(based on an index of human activity beneath the bridge), but there were no associations between 
bridges used and average daily vehicle traffic, amount of water under the bridge, age, height, 
length, or width of the bridge (McDonnell, 2001). 
From one to 25 Rafinesque’s big-eared bats were observed under concrete bridges in the De- 
Soto National Forest in Mississippi during the maternity season, with most solitary bats being adult 
males and maternity colonies averaging 5.6 ± 3.1 (SD) adult females (Trousdale and Beckett, 
2004). Radio-tracking studies revealed that some of these individuals also roosted in hollow trees 
(Trousdale and Beckett, 2005). In Louisiana, radio-tagged Rafmesque’s big-eared bats switched 
roosts frequently, also moving between concrete bridges or between bridges and hollow trees; dif¬ 
ferent roost locations of individual bats varied from 70 meters to 2.5 kilometers apart (Lance et al., 
2001). During summer Rafmesque’s big-eared bats occupied the same cistern long used as a win¬ 
ter roost in southern Illinois, but roosted in the warm upper portion rather than the lower part used 
during winter (Hoffmeister and Goodpaster, 1962). 
