ECHOLOCATION OF FLYING INSECTS BY THE BAT, CHILONYCTERIS PSILOTIS

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Abstract
Elements of acoustic orientation of C. psilotis during laboratory fruit-fly pursuits have been observed and analyzed. Such pursuits can be subdivided into search, approach, and terminal phases. The search phase is characterized by pulses of about 4 msec. duration repeated at a rate of about 18/sec. On detection of an insect, apparently by pulse-echo overlap (at a typical range of about 400-700 mm.), the approach phase begins, characterized by shortening (linear vs. time) pulse duration (to about 1.5 to 2.1 msec.) and shortening interpulse intervals. The approach phase (which lasts about 150-290 msec; 5-9 pulses) ends in a transition to the terminal phase[long dash]a rapid sequence of short (1-msec.) pulses produced at a rate of about 170/sec. The terminal phase lasts about 50-94 msec. and includes 11-18 pulses. Constant pulse-echo overlap of about 1.2 msec. characterizes the approach phase, implying distance measurement and overlap utility. During the terminal phase, pulse-echo overlap appears to be set at about 0.8 msec. The pulses of C. psilotis consist of a fundamental frequency, initially of about 21 kcps, with harmonics. During the search phase, the initial and final 1.5 msec of each pulse are of constant frequency but the central portion shows a frequency drop (for the fundamental, about 4 kcps). During a pursuit, the constant frequency portions are shortened and then fused into the frequency modulated part so that they are no longer recognizable beyond the early part of the terminal phase. Such a frequency pattern suggests possible mechanisms for recognizing and using pulse-echo overlaps.

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