ECHOLOCATION AND FORAGING BEHAVIOR OF THE LESSER BULLDOG BAT, NOCTILIO-ALBIVENTRIS - PREADAPTATIONS FOR PISCIVORY

We studied variability in foraging behavior of Noctilio albiventris (C hiroptera: Noctilionidae) in Costa Rica and Panama and related it to p roperties of its echolocation behavior. N. albiventris searches for pr ey in high (> 20 cm) or low (< 20 cm) search flight, mostly over water . It captures insects in mid-air (aerial captures) and from the water surface (pointed dip). We once observed an individual dragging its fee t through the water (directed random rake). In search flight, N. albiv entris emits groups of echolocation signals (duration 10-11 ms) contai ning mixed signals with constant-frequency (CF) and frequency-modulate d (FM) components, or pure CF signals. Sometimes, mostly over land, it produces long FM signals (duration 15-21 ms). When N. albiventris app roaches prey in a pointed dip or in aerial captures, pulse duration an d pulse interval are reduced, the CF component is eliminated, and a te rminal phase with short FM signals (duration 2 ms) at high repetition rates (150-170 Hz) is emitted. Except for the last pulses in the termi nal phase N. albiventris avoids overlap between emitted signals and ec hoes returning from prey. During rakes, echolocation behavior is simil ar to that in high search flight. We compare N. albiventris with its l arger congener, N. leporinus, and discuss behavioral and morphological specializations that can be interpreted as preadaptations favoring th e evolution of piscivory as seen in N. leporinus. Prominent among thes e specializations are the CF components of the echolocation signals wh ich allow detection and evaluation of fluttering prey amidst clutter-e choes, high variability in foraging strategy and the associated echolo cation behavior, as well as morphological specializations such as enla rged feet for capturing prey from the water surface.