Following are videos of two typical training sessions recorded, respectively, on February 6 and March 8, 2018.
Clap and Sing
As described here, both Mila and Eva previously had been trained behaviors referred to as “clap” and “sing”. In “clap” a dolphin surfaces and waves her pectoral fins. For “sing”, she surfaces and, with her head out of the water, produces rapid, pulsed vocalizations. For our experiment a trial is successful when Mila conveys the necessary information to Eva, Eva emerges out of the water and performs the behavior in front of her trainer. The following video, narrated by Benjamin, includes both “clap” and “sing”. Note that a portion of the soundtrack starting at 0:54s includes the hydrophone recording of Mila’s underwater vocalization of “sing” to Eva.
Following is a spectrogram of Mila’s underwater vocalizations to Eva from the above video. Each striped column represents a rapid pulsed segment of Mila’s “singing” vocalization to Eva.
It is well known that dolphins imitate other dolphins (and can even imitate humans) 7. For these two tasks the dolphins seem to have solved the communication problem by imitation. In “clap”, Mila has been observed submerging and waving her pectoral fins underwater. The subsequent water motion very likely is sensed by Eva and conveys the necessary information for her to know which behavior to perform. In the second trial in the video, “sing” was conveyed by Mila “singing” to Eva underwater, as heard in the video soundtrack at 0:54 seconds.
For this task Mila must submerge and call Eva to come over to her.
Following is a spectrogram of the underwater vocalizations from this trial. In contrast with the “sing” vocalizations, this time Mila vocalized to Eva with a repeating whistle. Almost immediately, Eva replied using a whistle with the same contour as Mila’s. For much of the time Eva was swimming over to Mila, the two dolphins chorused together with matching, overlapping whistles.
Results of the formal trials, performed in October 2018, are summarized here.
7. Herman, L.M., 2002. Vocal, social, and self-imitation by bottlenosed dolphins. In Dautenhahn, K. and Nehaniv. C.L., eds. Imitation in animals and artifacts. MIT Press, Cambridge, MA, USA 63-108.