Doppler-shift compensation in the Taiwanese leaf-nosed bat (Hipposideros terasensis) recorded with a telemetry microphone system during flight

Abstract

Biosonar behavior was examined in Taiwanese leaf-nosed bats (Hipposideros terasensis; CF-FM bats) during flight. Echolocation sounds were recorded using a telemetry microphone mounted on the bat's head. Flight speed and three-dimensional trajectory of the bat were reconstructed from images taken with a dual high-speed video camera system. Bats were observed to change the intensity and emission rate of pulses depending on the distance from the landing site. Frequencies of the dominant second harmonic constant frequency component (CF2) of calls estimated from the bats' flight speed agreed strongly with observed values. Taiwanese leaf-nosed bats changed CF2 frequencies depending on flight speed, which caused the CF2 frequencies of the Doppler-shifted echoes to remain constant. Pulse frequencies were also estimated using echoes returning directly ahead of the bat and from its sides for two different flight conditions: landing and U-turn. Bats in flight may periodically alter their attended angles from the front to the side when emitting echolocation pulses.

FM echolocating bats shift frequencies to avoid broadcast–echo ambiguity in clutter

“…2 H and I). We conclude, first, that these frequency shifts result from the bat's response, because the miniature microphone in the Telemike system protrudes forward from the Telemike circuit board on the bat's back and neck to occupy a recording position slightly forward of the external ears and just above the bat's open mouth (15)(16)(17). This location serves as a constant acoustic "vantage point" for measuring changes in FM1, so that the observed frequency differences can be attributed reasonably to the bat's vocalizations themselves.…”

“…The stationary ultrasonic microphone was more sensitive than the Telemike; it picked up echoes reflected back by the chains as well as the bat's broadcasts (Fig. 1 B-D) (15). Strong echoes were reflected by all the rows of chains over a span of 20-30 ms, corresponding to the depth of the chain array from the bat's position (Fig.…”

“…1 C and D. Sound Recordings. The bat's sonar pulses were recorded by a custom-made telemetry microphone (Telemike) mounted on the bat's upper back and head (15)(16)(17). It registered the bat's FM broadcasts (Fig.…”

“…Here, we combine two recently introduced experimental methodsradio telemetry of sounds from the flying bat for very stable recording of the transmitted signals (15)(16)(17) in tandem with flight tests using an extended array of obstacles during which bats emit sounds at sufficiently short IPIs to create the conditions for ambiguity (12). The bat's response to ambiguity caused by overlap of extended echo streams is specific: Whenever ambiguity occurs (IPIs shorter than ESDs), the bat shifts the frequencies of the FM sweep upward in the first broadcast and downward in the second broadcast by several kilohertz (ΔF) in proportion to the degree of overlap (IPI minus ESD).…”

Radiation pattern of echolocation pulse in Taiwanese leaf-nosed bat, Hipposideros terasensis

“…In our recent study, we estimated the position of the target listened to by the Taiwanese leaf-nosed bat (Hipposideros terasensis) during flight by evaluating call parameters: such as frequency and the interemission interval [1]. By comparing these data with the three-dimensional coordinates of the flight path, we found that bats in flight may periodically alter their direction of attention from the front to the side during direct approaches to the target wall.…”