Am. Boonman et al., PREY DETECTION IN TRAWLING INSECTIVOROUS BATS - DUCKWEED AFFECTS HUNTING BEHAVIOR IN DAUBENTONS BAT, MYOTIS-DAUBENTONII, Behavioral ecology and sociobiology, 44(2), 1998, pp. 99-107
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.