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Many species of bats use frequency-modulated (FM) “chirps” to sense their environment by sonar. A method was developed for locating the chirps of individual bats while simultaneously tracking the positions of multiple bats in infrared videos. Three microphones and one infrared camera recorded multiple bats flying above a small open pool. Azimuth and elevation was computed for all chirps in a given 15-s interval and matched to position coordinates given by the infrared camera. By grouping spatially continuous sets of chirps, each individual bat's chirp pattern can be obtained. This combination of visual and acousticinformation will provide new insight into the behavior and sonar capabilities of FM ranging bats.

Behavioral evoked vocal responses of male bullfrogs (Rana catesbeiana) are sensitive to slight disruption of the 1st harmonic periodicity in synthetic calls produced by changes in component phase. We implemented a computational model that estimates stimulus period from autocorrelation functions (all-order interval histograms) of auditory nerve responses aligned in time across frequency channels. Output of the model shows differences between stimuli in a manner reflecting behavioral data. In contrast, peri-stimulus-time histograms aligned across channels do not clearly reflect behavioral responses. The estimate of stimulus period derived from time-alignment autocorrelation shown here is similar to display of pitch images in models based on mammalian data.

Infrared cameras and ultrasonic microphones were used to record big brown bats (Eptesicus fuscus) flying in natural conditions at night while they hunted for insects. As expected, bats avoided obstacles while flying through vegetation and intercepted flying prey in the open. But bats also appeared to capture insects near and possibly on the ground and near or in vegetation, flew low over water to drink, and pursued each other in aerial “dogfights.” In less than a minute, the same bat often used echolocation for several different tasks, showing a wider repertoire of sonar-guided behavior than revealed by previous observations limited to seeing bats flying against the evening sky or being photographed in fixed fields-of-view.

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...

Bullfrog eighth‐nerve fibers operate as envelope detectors, showing significant phase‐locking to amplitude modulation (AM) rates as high as 800 Hz. A computational model that estimates stimulus period from all‐order interval histograms (autocorrelation functions) aligned in time across frequency channels mimics fiber responses. The use of autocorrelation implies a mechanism based on delay lines or neural coincidence detection. The goal of this study was to determine the relevance of such a model in predicting responses of neurons in bullfrogs auditory midbrain (torus semicircularis) to AM stimuli. Modeled output of peripheral fibers was passed through a series of delay lines varying in latency, and then compared with actual midbrain data. There is a great diversity in representation of AM in the auditory midbrain, and this diversity is related to response latency and recording location. Neural responses from the cell sparse zone in the caudal midbrain were well‐matched by a delay line mechanism, although ...

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.

Big brown bats resolve delays of overlapping FM biosonar echoes down to 2–4 μs. They must use a time‐frequency representation because integration time is ∼350 μs. The bat may have ∼25 000 auditory‐nerve fibers from ∼1000 inner hair cells tuned to frequencies from 10 to 100 kHz. If auditory‐nerve latency jitters of 50–100 us are averaged across frequencies, estimated timing accuracy could be as good as ∼0.5 μs. Monaural timing pathways to the inferior colliculus have jitters no worse than the auditory nerve and also could convey a timing accuracy as good as ∼0.5 us. In the inferior colliculus, frequency‐domain responses to interference notches register delay separations down to 5–6 μs for two‐point resolution. Time‐domain latency jitter for tone bursts increases sharply in the IC, but over half of the cells respond to FM pulses and echoes in synthetic pursuit sequences with latency jitters of only 100–500 μs. This ∼2–5x increase in intrinsic jitter in the IC is accompanied by a disproportionate increase...