Daubenton's feeding strategy
A well-known Dutch study (Boonman et al, 1998) dealt with the effects of water surface clutter on the hunting behaviour of DB. A trawling bat species, hunting for insects that are close to, or rest on, the water surface. The researchers focused on clutter caused by plants (although they stated that clutter might also be caused by wind and rain, since both give rise to ripples on the water surface); the hunting behaviour of Daubenton's bats and on the ultrasound-detecting properties of the water surface.
The study revealed the following that Daubenton's bat avoids water surfaces covered with duckweed. Measurements with ultrasonic signals show that a water surface covered with weed returns a much stronger background echo at small angles (i.e. parallel to the water surface) compared to an uncovered water surface. It seems likely that a cover of weed on the water surface interferes with prey detection by masking the echoes returning from prey.
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| Algae on water surface Filter Bed 7 May, 2012. |
The fact that Daubenton's bats avoid water surfaces covered with plants is likely to have ecological implications. Some floating freshwater plants such as duckweed, Cladophora algae and Potamogeton pondweed, for example, are abundant where there is organic pollution or high nutrient loading. According to the results of the study, plant cover on the water surface can make a pond unsuitable as a hunting site for Daubenton's bats. Eutrophication of ponds and lakes might therefore exert a negative effect on populations of Daubenton's bat counteracting a positive effect due to an increase in the number of chironomids.
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