Pallid bats (Antrozous pallidus) are unusual among vespertilionids (the most common and diverse family of bats in temperate regions of the world) in that they often emit a loud, partially audible social call several times in rapid succession while in flight. This social call appears to function as a contact call in that it is frequently given when bats return from foraging and perform circular flights before entering a crevice roost. In this dissertation, I examine the functional and social significance of this calling behavior by free-flying pallid bats in central Oregon using a combination of observations, audio recordings, audio playbacks, acoustic analysis, and genetic marker analysis. In chapter 1, I found that bats respond to the calls of conspecifics and that call structure is unique to individuals and stable through time, which makes these calls well-suited for roostmate recognition. In chapter 2, I found significant genetic structure among colonies based on sequence variation at the mitochondrial DNA control region but very little structure among colonies for nuclear microsatellites. These data are indicative of female philopatry with male-mediated gene flow and highlight the potential that calls may function in the maintenance of multigenerational social groups. Finally, in chapter 3, I utilized genetic markers to investigate relatedness among individuals sharing a roost and the extent to which call variation encodes information about relatedness to examine whether calling behavior may assist in maintaining social bonds as individuals switch roosts. I found that while average colony relatedness was low, bats roost with a greater proportion of relatives than expected by chance. In addition, I found that contact call structure encodes information about matrilineal relationship and relatedness as well as individual identity. Overall, these results suggest that calling behavior in pallid bats is important in maintaining social structure at maternity roosts. Given the high roost lability and nocturnal environment of pallid bats, this study offers important insight into how animals in fluid societies mediate interactions with groupmates using acoustic signals.