THE SENSITIVITY OF ECHOLOCATION IN BATS

Abstract

The distances at which Myotis lucifugus react to small wire obstacles has been measured by photographically registering the distance from a row of wires at which the flying bat first increases its pulse repetition rate, or decreases the interval between successive pulses. The average distance at which this vocal reaction occurred was 215 cm for 3 mm wires, 185 cm for 1.07 mm, 150 cm for 0.65 mm, 120 cm for 0.54 mm, 105 cm for 0.28 mm and 90 cm for 0.18 mm. The wires were vertical and spaced 30 cm apart across the middle of a flight room 10 meters long. A conservative correction for reaction time of the bat and for the acoustic delay between its mouth and the microphone indicates that the distance of detection of such wires is at least 10 cm greater than the above distances of first reaction. Since small wires can be detected at 5500 times the diameter of the wires, and well before there is any noticeable changes in the flight pattern, it appears likely that larger objects are detected at considerably greater distances.