Echolocation calls of bats vary in design, and their structure often reflects the ecological and sensory requirements of the bats (Neuweiler, 1989; Fenton, 1990). Individual bats can modify their calls according to conditions: for instance, in confined spaces, calls may become shorter and of broader bandwidth (e.g. Kalko and Schnitzler, 1993). Individual flexibility in echolocation calls is clearly illustrated during feeding attempts of bats that feed on aerial prey or on prey on the water surface (e.g. Hartley et al., 1989; Surlykke et al., 1993). When searching for prey, the bat emits search-phase calls. On detection of the prey, pulse repetition rate increases and pulse duration and interpulse interval (IPI) decrease during the approach phase, reaching extreme values during the terminal phase of the buzz immediately prior to capture (Griffin et al., 1960). In many species, the terminal phase can be subdivided into the phases ‘buzz I’ and ‘buzz II’. An abrupt fall in call frequency typically marks the onset of buzz II (e.g. Kalko and Schnitzler, 1989; Surlykke et al., 1993). Echolocation calls emitted during the search phase are designed for detecting targets, whereas calls emitted during the approach phase are modified to provide more information on target location and type (Simmons et al., 1979). The function of signals emitted during the terminal phase is to provide information on a prey item’s position immediately prior to capture (Fenton and Bell, 1979). The terminal phase of echolocation behaviour is synonymous with the phrase ‘feeding buzz’ (e.g. Griffin, 1958; Acharya and Fenton, 1992), but here we use the phrase ‘terminal buzz’ since it is often unclear whether the capture attempt was successful. The structure of the terminal buzz may vary according to the nature of prey attacked and whether the capture attempt is successful. In Lasiurus borealis and L. cinereus, the duration of the terminal buzz was not related to prey size, but the silent period after the buzz (which we call the ‘post-buzz pause’) was longer after successful than after unsuccessful capture attempts (Acharya and Fenton, 1992). Here, we develop some hypotheses about how the structure of various components of the terminal buzz should vary in relation to feeding behaviour, and test these predictions both in the field and in the laboratory by studying prey capture from the water surface (trawling) in Daubenton’s bat Myotis daubentonii. M. daubentonii is classified in the subgenus Leuconoe on morphological characteristics. Many species in this subgenus 1793 The Journal of Experimental Biology 202, 1793–1801 (1999) Printed in Great Britain © The Company of Biologists Limited 1999 JEB1951 During prey-capture attempts, many echolocating bats emit a ‘terminal buzz’, when pulse repetition rate is increased and pulse duration and interpulse interval are shortened. The buzz is followed by a silent interval (the post-buzz pause). We investigated whether variation in the structure of the terminal buzz, and the calls and silent periods following it, may provide information about whether the capture attempt was successful and about the size of prey detected – detail that is valuable in studies of habitat use and energetics. We studied the trawling bat Myotis daubentonii. The time between the first call of the approach phase and the end of the terminal phase was not related to prey size in the laboratory. The last portion of the terminal buzz (buzz II) was shortened or omitted during aborted capture attempts. Both in the laboratory and in the field, the mean interpulse interval immediately after the terminal buzz (post-buzz interpulse interval) was longer in successful captures than in unsuccessful attempts. In the laboratory, the post-buzz pause was longer after successful captures than for unsuccessful attempts, and the minimum frequency of the first search-phase call emitted after the buzz (Fmin ) was higher than that of the last such call prior to the buzz. These effects were not apparent in field data. Both in the laboratory (85 %) and in the field (74 %), significant discrimination between successful and unsuccessful capture attempts was possible when the duration of the post-buzz pause, post-buzz interpulse interval and F min were entered into a discriminant analysis. Thus, variation in the echolocation calls of bats during prey-capture attempts can reveal substantial information about capture success and prey size. Key words: echolocation, bat, Myotis daubentonii, prey capture, sonar. Summary Introduction ECHOLOCATION BEHAVIOUR AND PREY-CAPTURE SUCCESS IN FORAGING BATS: LABORATORY AND FIELD EXPERIMENTS ON MYOTIS DAUBENTONII ADAM R. C. BRITTON AND GARETH JONES* School of Biological Sciences, University of Bristol, Woodland Road, Bristol BS8 1UG, UK *Author for correspondence (e-mail: Gareth.Jones@bris.ac.uk) Accepted 1 April; published on WWW 8 June 1999