Observation studies based on echolocation click signals of Irrawaddy dolphins in Chilika lagoon

A resident population of Irrawaddy dolphins, Orcaella brevirostris, in Chilika lagoon in eastern India has been recently monitored based on their echolocation clicks. The free‐ranging animals were monitored over several days in their natural habitat. A horizontal three‐hydrophone line array was used for click data collection and off‐line analysis of click trains to obtain underwater movements in shallow water of typical depth less than 3 m. The lagoon waters being placid provided a good surface echo that has been used to obtain depth information of the individual click sounds. This paper augments previous data on the broadband click characteristics [S. M. Van Parijs, G. J. Parra, and P. J. Corkeron, J. Acoust. Soc. Am. 108, 1938–1940 (2000)] and also provides a glimpse into the individual behavior of the dolphins. An estimate of the click lag time of the animal’s biosonar has also been obtained for the first time for a free‐ranging animal.