Behavioral and ecological aspects of gleaning by a desert insectivorous bat Antrozous pallidus (Chiroptera: Vespertilionidae)

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1. The feeding behavior of Antrozous pallidus was studied in the field. To determine the sensory basis of prey location, and patterns of prey selection, bats were presented with live, wing-clipped moths, the sounds of fluttering moths, and the mating calls of crickets. Diet was determined through analysis of culled parts and feces collected at night roosts. 2. Flying bats located and captured prey which were on the ground. Echolocation calls were produced while searching for prey, but never during approach or attack, and I never saw A. pallidus capture flying prey. 3. In this study A. pallidus fed primarily on medium-sized to large moths, but other prey included orthopterans, beetles, neuropterans and chilopods, and, in one case, a pocket mouse (Perognathus flavus). A range of prey sizes was taken, but most prey (44%) were medium to large (≧20 mm body length). In prey selection experiments A. pallidus captured mediumsized prey in the least time; larger prey required greater handling time and smaller prey took longer to locate. While this species appears to be foraging optimally, maximizing energy intake by taking larger prey, such prey selection is most likely the result of prey conspicuousness. 4. Prey were located by the rustling sounds they produced on the ground. A. pallidus responded to the sounds of concealed prey, and to the tape recorded sounds of prey, and ignored dead or stationary prey. Bats did not respond to otherwise attractive sounds produced in heavy cover, and did not investigate the calls of crickets. All orthopterans observed in this study called from concealed places, usually from within heavy, thorny cover. 5. I conclude that A. pallidus use echolocation, and perhaps vision, to assess habitat and avoid obstacles, but locate prey by listening to their sounds. Echolocation is not used during prey capture, perhaps to avoid warning tympanate prey of their approach. These bats are able to discriminate between sounds which probably indicate food (i.e. rustlings in open areas) from sounds which offer no reward (orthopteran mating calls).