Daily and Seasonal Patterns of Singing by the Mexican Free-Tailed Bat, Tadarida brasiliensis

Abstract

Singing is a specialized vocal behavior that supports courtship and territoriality but costs energy and time. Singing behaviors are well documented in the Mexican free-tailed bat, Tadarida brasiliensis, but many important questions about the functional significance of singing in this species remain unanswered. To better understand how singing benefits this species we analyzed daily and seasonal temporal patterns of singing in both a natural and a captive colony for extended periods of time and measured the average call and song rates over the course of seven days and over one entire year. Analyses revealed that under natural conditions singing was most prevalent at onset of the spring and fall migration periods but also continued at a less frequent rate throughout the summer months. Singing rates were highest during the spring mating season, but singing also continued through the summer months in exclusively male colonies. In a natural roost, males sang the most just before sunrise, but also sang prolifically just after sunset and sporadically throughout the night. This pattern suggested that singing patterns were driven by the activity of conspecifics leaving and returning to the roost, and also indicated that singers may spend less time foraging than their roost-mates. We tested this by measuring movements and singing patterns in a captive colony, where roost-mates were confined to flying around the vivarium at night. Under these conditions captive bats sang continuously at high rates throughout the night. We propose that singing by T. brasiliensis evolved initially to facilitate migration by facilitating more rapid localization of roosts by bats passing through novel territories, particularly just before sunrise. Singers sacrifice foraging time but may gain a reproductive advantage by attracting more bats to their roost during the spring mating season, which may explain why males but not females of this species sing.