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Echolocating bats (Pipistrellus, Myotis) sometimes fly in dense swarms for 1–2 h over desert water sources. Swarming is different from streaming at caves or roosts because ∼10–100 bats staying within a small volume (∼1000 m3) for an extended time rather than transiting. We study swarming using thermal infrared video cameras and a three‐microphone acoustic array. Swarming bats emit a steady stream of short (∼2 ms) FM sonar sounds with nearly identical sweeps and a collective duty‐cycle approaching 100%. Surprisingly, given the tendency to think in terms of bats in close proximity deliberately varying their signals for jamming avoidance, the signals of swarming bats are very similar. Video/acoustic tracks reveal no sign of mutual interference or collisions. It is not obvious whether bats gather to drink or to feed on insects, which also congregate near the water, or whether social behavior predominates. Some drinking occurs throughout the swarming period, but the occurrence of captures during swarming is ne...

A method for localizing sounds was applied to simultaneously reconstruct the emission pattern and flight path of echolocating bats. An infrared camera and an array of three microphones were used to record simultaneous audio signals and video images of groups of bats while foraging. The bats studied (Eptesicus, Myotis, Pipistrellus) use frequency sweeping ‘‘chirps’’ in the 25–45 kHz to 100–120 kHz band for echolocation. Cross correlation of the bats’ chirps was used to find delays in chirp arrival time between microphones in the array. These delays were then used to locate the chirps’ direction. A time‐series of these coordinates was found, then calibrated to pixel points of the corresponding infared video recording to reconstruct the flight path and chirp pattern for each of the bats over 15‐s intervals. By providing simultaneous emission and position information throughout time, this method addresses questions about dynamic adaptation of the emission patterns of bats to the acoustic environment. Simultaneous adaptation between bats flying in groups is particularly interesting. An accompanying abstract discusses the implications of these findings for the current paradigm of information processing in the FM bat’s auditory pathway.

Using an infrared body‐heat‐imaging video camera and a microphone array, we made field recordings of FM echolocating bats (Eptesicus, Myotis, Pipistrellus) while they deployed their sonar alone or in company with other bats. We observed cruising flights of bats in transit from roosts to feeding areas, bats flying low over water for drinking or hunting, and aerial interception maneuvers in open areas (larger insects were visible, too). However, we also recorded frequent captures of insects on or near the ground, flights into vegetation to capture beetles, and groups of bats flying in close proximity while drinking or making aerial captures of insects. Bat‐to‐bat dogfights were common, some involving two or more bats diving and violently maneuvering close to the ground or near vegetation. For single bats or several bats not very close to each other, we recorded typical interception maneuvers with pursuit sequences consisting of search‐, approach‐ (tracking‐), and terminal‐stage signals. By reconstruction of flight and emission patterns, we found that bats flying in close proximity alternated their broadcasts, and large aggregations of bats feeding close together perpetually emitted sounds characteristic of the mid‐approach stage, with short durations, high repetition rates, and no discernible terminal stages.