The final call: evidence for stereotyped whistle of one dying common dolphin (Delphinus delphis) in Argentina

Abstract

Signature whistles are stereotyped and individually distinctive acoustic signals used as individual recognition calls, for maintaining group cohesion and during stressful situations. Here, it's proved the occurrence of stereotyped whistles and how it changes, by an isolated adult female of short-beaked common dolphin (Delphinus delphis) kept in rehabilitation. Twenty-three hours of continuous recordings were collected until the dolphin death for hepatitis. A total of 64 whistles were analyzed along the hours and only an ascending-descending frequency contour was detected. The number of whistles decreased during the rehab period. Whistles showed a mean peak frequency contour (PFC) of 9.45 ±1.09 kHz, a mean maximum frequency value of 12.0.4 ±1.65 kHz, a mean minimum frequency of 7.04 ±1.16 kHz, a mean duration of 0.75±0.27 seconds and a number of harmonics ranging from 1 to 3. The low variability of whistles parameters along the hours and the only whistle contour found in an isolated and stressed dolphin support the hypothesis of stereotyped whistles. It is the first evidence of the use of this signal by Delphinus delphis in Southwestern Atlantic Ocean (SWAO) and is first step to understand the sound production related to the rehabilitation process.