PREY DETECTION IN TRAWLING INSECTIVOROUS BATS - DUCKWEED AFFECTS HUNTING BEHAVIOR IN DAUBENTONS BAT, MYOTIS-DAUBENTONII

Daubenton's bat, a trawling vespertilionid bat species, hunts for inse cts that fly close to, or rest on, the water surface. During summer, m any ponds at which Daubenton's bats hunt become gradually covered with duckweed. The purpose of this study was to investigate the effects of duckweed cover on the hunting behaviour of Daubenton's bats and on th e ultrasound-reflecting properties of the water surface. Our study rev ealed the following. (1) Daubenton's bat avoids water surfaces covered with duckweed. (2) Prey abundance was related to the number of foragi ng Daubenton's bats but was independent of duckweed cover. (3) When me alworms were presented among standardized amounts of duckweed to natur ally foraging Daubenton's bats, they caught significantly less mealwor ms when the duckweed cover was increased. (4) Measurements with ultras onic signals show that a water surface covered with duckweed returns a much stronger background echo at small angles (i.e. parallel to the w ater surface) compared to an uncovered water surface. It seems likely that a cover of duckweed on the water surface interferes with prey det ection by masking the echoes returning from prey. (5) It was relativel y difficult for the bats to discriminate small patches of duckweed fro m mealworms. The proposed discrimination mechanism for this trawling b at species suggests that single duckweed patches can also be mistaken for natural prey by Daubenton's bats.