Detection of insect wing beats by the bat, <i>Pteronotus parnellii</i>

Abstract

An investigation was made into one possible use of the “pure tone” portion of the echolocation signals of Pteronotus parnellii parnellii (Gray). It was verified that the echo of a constant frequency 60-kHz signal from a wax moth (Galleria mellonella) contains instantaneous Doppler shifts of as much as 300 Hz due to the wing motion. The complexity of the wing motion produces these Doppler shifts for arbitrary aspect angle. The sharp sensitivity peak in the cochlear microphonic (CM) tuning curve of P. parnellii [G. D. Pollack et al., Science 176, 66–68 (1972)] could be used to detect the wing beat Doppler shifts. The frequency deviations would be converted into amplitude deviations. This effect was verified by stimulating bats with the artificial moth echo signal with the “carrier” frequency adjusted to the center of the particular bats' sensitivity peak and monitoring the CM potential. Large amplitude fluctuations occur as the frequency sweeps back and forth through the sensitivity peak. This mechanism may explain the flight speed Doppler compensation in the echolocation signals.