Use of Bridges by Bats (Mammalia: Chiroptera) in the Rio Grande Valley, New Mexico‪.‬

Humans have caused declines or jeopardized populations of bats throughout the United States and world (Hill and Smith, 1984; O'Shea and Bogan, 2003), but certain human influences also have benefited bats, such as establishment of water sources in arid regions (e.g., stock tanks; Geluso, 1978; Tuttle et al., 2006), implementation of educational programs that emphasize the value of bats and encourage their protection (Fenton, 1997), and construction of structures used for shelter (e.g., buildings, bridges, culverts, tunnels, and mines; Kunz, 1982; Fenton, 1997). Many human-made structures function as roosting sites for many species (e.g., Barbour and Davis, 1969; Davis and Cockrum, 1963; Sandel et al., 2001), although most shelters were not intended to house bats. Throughout the United States, bridges commonly are inhabited by many species of bats, because these structures serve as various types of roosts, including daytime shelters (Stager, 1943; Davis and Cockrum, 1963; Fraze and Wilkins, 1990; Arnett and Hayes, 2000; Lance et al., 2001; Trousdale and Beckett, 2002; Feldhamer et al., 2003; Keeley and Keeley, 2004; Ferrara and Leberg, 2005), night roosts (Hirshfeld et al., 1977; Lewis, 1994; Adam and Hayes, 2000), maternity roosts (Davis and Cockrum, 1963; Trousdale and Beckett, 2002), bachelor roosts (Davis and Cockrum, 1963), and transient roosts (Davis and Cockrum, 1963; Fraze and Wilkins, 1990). Despite the number of species and various types of roosts observed in bridges, documentation and preservation of bridges as important roosting sites are minimal in many states. Protection of bridges is important because they provide places for important life-history functions such as copulation, bearing and raising of young, consumption and digestion of food, rest, grooming, and hibernation. Humphrey (1975) proposed that availability of roosting sites might be a limiting resource for bats, and when roosts are absent or removed, bats may disappear from areas or their abundance, distribution, and demographics may be altered (Constantine, 1967; Findley, 1987; Lewis, 1995; Fenton, 1997).