Amazon river dolphins (Inia geoffrensis) modify biosonar output level and directivity during prey interception in the wild

TitleAmazon river dolphins (Inia geoffrensis) modify biosonar output level and directivity during prey interception in the wild
Publication TypeJournal Article
Year of Publication2017
AuthorsLadegaard, Michael, Jensen Frants Havmand, Beedholm Kristian, da Silva Vera Maria Ferr, and Madsen Peter Teglberg
JournalThe Journal of Experimental Biology
Volume220
Pagination2654
Type of Article10.1242/jeb.159913
EndNote Rec Number11654
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 predicted 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 is also seen in captive toothed whales and bats, thus resulting in a larger ensonified volume around the prey, probably aiding prey tracking by decreasing the risk of prey evading ensonification.