Lutra 50(2)_Van De Sijpe & Holsbeek_2007

Hunting strategy and tympanate moth predation by the pond bat (Myotis dasycneme)

Visual observations of moth predation by pond bats (Myotis dasycneme) are described and related to typical secondary echolocation and flight behaviour patterns. When hunting over canals and rivers, the common search phase of pond bats combines low-level flight over the water surface with an quasi uninterrupted series of frequency modulated echolocation calls. During the season that moths become available the bats gradually switch to a faster and linear search flight, regularly interrupted by sudden rises and attacks upon moths. Observations of power dives of moths upon bat approaches reveal that these attacks are often aimed at tympanate moths. The bats counter the moths’ escape reactions by additional aerial attacks or by an immediate switch from aerial hawking to trawling in response to the power-diving prey dropping to the water surface. During these search flights, bats switch between two distinct echolocation signals, the first predominantly frequency modulated, the second having a more pronounced QCF ending, with both differing from the basic trawling echolocation signal. In this fast aerial hawking search phase, pond bats typically switch between sequences of high intensity pulses and sequences of silences or possible stealth/whispering mode, creating a discontinuous call pattern. These sound sequences always include narrowband signals of a high intensity and long duration, increasing the detection distance to larger prey items. We assume that this discontinuous echolocation pattern facilitates the bats in successfully approaching tympanate moths by delaying or counteracting the moths ability to identify bats from a distance