MERCURY-VAPOR LAMPS INTERFERE WITH THE BAT DEFENSE OF TYMPANATE MOTHS(OPEROPHTERA SPP. GEOMETRIDAE)

Bats often forage near streetlamps, where they catch moths in particul ar. At least two hypotheses may explain the apparent increase in the a vailability of moths to bats feeding around streetlamps: (1) the moths become concentrated near the light and therefore more profitable to e xploit; and (2) the light interferes with the moths' evasive flight be haviour. We tested the second of these hypotheses by exposing flying m ale winter moths, Operophtera spp., to bursts of ultrasound (26 kHz, 1 10 dB sound pressure level) from an electronic source. The light from a 125 W mercury vapour lamp had a quantitative effect on the moths' ev asive flight response at close range (within ca 4 m), inhibiting it to tally in nearly half (43%, N=125) of the cases. By contrast, moths fly ing in the surrounding woodland and without interference from the lamp always responded to the sound. Streetlamps of the mercury vapour type (white lamps) thus interfere with the defensive behaviour of moths an d presumably increase their vulnerability to echolocating bats. This m ay have implications for the conservation of both moths and bats. (C) 1998 The Association for the Study of Animal Behaviour.