Maternal aggressive contact vocalizations in captive bottlenose dolphins (Tursiops truncatus): Wide‐band, low‐frequency signals during mother/aunt‐infant interactions

Abstract

AbstractThe mother‐infant bond in bottlenose dolphins is critical to infant survival and has been reported to last from 3‐10 years in both captive and wild populations. Little information on mother‐infant communication during early development has been collected. This paper reports on a newly discovered dolphin vocalization, termed thunk, which is predominantly used by mothers toward infants. Four mother‐infant pairs and one aunt‐infant pair were the subjects for this study. Methods included a focal animal sampling technique using 2.5 min interval and event/continuous sampling regimes on audio‐ or videotape. Results indicated that thunks are produced by mothers or aunting females during infant departures (distances greater than 5 feet) and are frequently followed by disciplinary activity by the mother or aunt. In addition, thunks appeared to cease at approximately 9‐10 months after birth, concurrent with a decrease in infant dependence. Thunks also were analyzed acoustically for frequency and duration parameters. Thunks have a harmonic structure with an energy peak in the 273–350 Hz range and ranged from 129–5,556 Hz in frequency and from 21–171 ms in duration. They appear to function as aggressive contact vocalizations produced by mothers and other adult females toward infants in order to maintain infant proximity. © 1995 Wiley‐Liss, Inc.