Light tags are used to study bats because they allow visual observations of these nocturnal animals. In this study, we document changes in roosting behaviors of the greater spear-nosed bat, Phyllostomus hastatus, when light tags were applied. Roost behaviors of eight light-tagged female bats were recorded using reflectance infrared videography and compared to roost behaviors of untagged harem members. Light-tagged females were recipients of more aggressive interactions from their harem mates than untagged individuals; they were more often chased away from a group, moved away from (disengaged), and rejected by harem members than were untagged individuals. In addition, light-tagged bats spent significantly more time roosting alone than untagged individuals. These findings indicate that roosting behaviors of P. hastatus were altered when light tags were applied. Our results clearly document altered behavior in P. hastatus as a result of the application of light tags, and consequently caution should be used when applying light tags to this and others bat species when investigating roosting behavior.