Experimental evidence for voluntary vocal control in an aged Pacific white-sided dolphin

Voluntary vocal control is a fundamental component underlying vocal learning in animals. However, quantitative reports on the establishment of voluntary vocal control during training have been limited. In this study, we experimentally examined the trainability of voluntary vocal control in an aged male Pacific white-sided dolphin via operant conditioning with differential reinforcement of vocal responses. The dolphin was trained to suppress vocalizations during a standby condition and to selectively produce two call types (burst and chorus) in response to two distinct visual cues. Importantly, the learning process of the chorus, which the dolphin had not previously been trained to produce in response to cues, was evaluated. The learning criterion was reached after 30 training days and 42 sessions over a 126-day period, corresponding to approximately 1.5-2.5 h of systematic training. Results from the test phase demonstrated that the individual could voluntarily produce specific call types or suppress vocalizations in response to visual cues. These findings provide quantitative evidence of voluntary vocal control, a fundamental component of vocal usage learning, in an aged Pacific white-sided dolphin.