Dear colleagues, For those of you interested in toothed whale biosonar, we wish to draw attention to a new publication in Journal of Experimental Biology. We have investigated the biosonar beam dynamics and source parameter adjustments that Amazon river dolphins use as they approach and intercept prey in the first study to report on-axis source parameters for wild toothed whales engaged in prey capture. The prey was tied to a hydrophone, which was lowered in front of a star shaped seven-hydrophone array. If you would like to see an example of one of these prey captures then please follow this link (the camera was located slightly above the hydrophone array centre): http://movie.biologists.com/video/10.1242/jeb.159913/video-1 Amazon river dolphins (Inia geoffrensis) modify biosonar output level and directivity during prey interception in the wild Michael Ladegaard, Frants Havmand Jensen, Kristian Beedholm, Vera Maria Ferreira da Silva, Peter Teglberg Madsen Journal of Experimental Biology 2017 220: 2654-2665 Abstract Toothed whales have evolved to live in extremely different habitats and yet they all rely strongly on echolocation for finding and catching prey. Such biosonar based foraging involves distinct phases of searching for, approaching, and capturing prey, where echolocating animals gradually adjust sonar output to actively shape the flow of sensory information. Measuring those outputs in absolute levels requires hydrophone arrays centred on the biosonar beam axis, but this has never been done for wild toothed whales approaching and capturing prey. Rather, field studies make the assumption that toothed whales will adjust their biosonar in the same manner to arrays as they will when approaching prey. To test this assumption, we recorded wild botos (Inia geoffrensis) as they approached and captured dead fish tethered to a hydrophone in front of a star-shaped seven-hydrophone array. We demonstrate that botos gradually decrease interclick intervals and output levels during prey approaches, using stronger adjustment magnitudes than extrapolated from previous boto array data. Prey interceptions are characterised by high click rates, but although botos buzz during prey capture, they do so at lower click rates than marine toothed whales, resulting in a much more gradual transition from approach phase to buzzing. We also demonstrate for the first time that wild toothed whales broaden biosonar beamwidth when closing in on prey, as it is also seen in captive toothed whales and in bats, thus resulting in a larger ensonified volume around the prey, likely aiding prey tracking by decreasing the risk of prey evading ensonification. The paper is available here: http://jeb.biologists.org/content/220/14/2654 A copy of the paper can also be requested by emailing michael.ladegaard@bios.au.dk<mailto:michael.ladegaard@bios.au.dk>. On behalf of the co-authors, Michael Ladegaard Michael Ladegaard PhD student Mobile: (+45) 4076 4035 Email: michael.ladegaard@bios.au.dk<mailto:mail@au.dk> Web: Michael Ladegaard<http://pure.au.dk/portal/en/persons/id(7365cdb9-ab50-4488-9839-034eb5c3cd5e).html> Department of Bioscience - Zoophysiology Aarhus University C. F. Møllers Allé 3, building 1131 8000 Aarhus C Email: mail@au.dk<mailto:mail@au.dk> Web: http://bios.au.dk/en/