Observations on the Development of Echolocation in Young Bottlenose Dolphins

Abstract

With the birth of two male bottlenose dolphins (Tursiops truncatus) with a 72 hour period into our research colony we began a two year program of systematic observation and recording of the ontogeny of their vocal and non-vocal behavior and communication. While pursuing this program we were fortunate to obtain instances of apparent echolocation by the young animals during the fourth postnatal week. Previously, the earliest instance of dolphin echolocation was reported in a sixty-day old bottlenose dolphin by Carder and Ridgway (1983). They observed head scanning movements concurrent with high energy pulses with peak frequencies ranging from 33 to 120 kHz with 3-dB bandwidths of 28-81 kHz. The appearance of sonar-like pulses by our animals at so early an age prompted us to review the acoustic and behavioral data we had compiled for the period extending from birth to postnatal day 40 when the infant and adult pulses were indistinguishable to 16 kHz, the limits of our recording and analysis equipment (see Methods). TI1US, we can report here on a wide range of behavioral development concurrent with the ontogeny of echolocation as it occurred within a captive but social milieu. Additionally, we can suggest and provide examples of vocalizations which may play a role as precursors to normal echolocation