Foraging activity and food resource use of Brazilian free-tailed bats, Tadarida brasiliensis (Molossidae)

We studied foraging activity and food resource use of Brazilian free-tailed bats, Tadarida brasiliensis, from a large maternity colony near Uvalde, Texas. We recorded echolocation calls of bats at replicate sites in towns, cropland, and ranches and quantified the proportions of signal-receiving time, the numbers of feeding buzzes, and the mean attack attempts per unit of activity time to evaluate habitat use by bats. Food habits of the bats were determined from fecal samples, and the composition and relative abundance of various insect orders in the three habitats were assessed using light traps. Towns with mercury-vapor type street lamps appeared to be important feeding areas for the bats, where they exhibited higher foraging activity and attack rates than over cropland or ranches. The common use of street lamps over towns, however, could have affected the efficiency of our traps in insect assessment; towns exhibited lower relative insect abundance than the other two habitats. Insect abundance did not differ between ranches and cropland, but a decline in relative insect abundance occurred in pre-dawn periods over cropland, which correlated to a higher bat activity per unit time over ranches than on cropland. The bats also displayed higher attack rates, and had a broader diet, in evening than in pre-dawn periods. The diet of bats contained 12 orders of insects, which accounted for 80% of insect orders captured in traps. At the ordinal level, the relative importance of these prey in the bats' diet strongly correlated to those sampled by the traps. The differences in relative abundance of major insect orders between midnight and pre-dawn sampling also correlated to those in percent volumes of respective insect orders in the bats' diet. These results agree with our prediction and suggest an opportunistic foraging mode for this species.