-San Antonio, Texas-
In July of 1987, a Dall’s porpoise (Phocoenoides dalli), with her umbilical cord still attached, stranded in Bodega Bay, California. She was transported to Marine World Africa, USA for treatment of pneumonia. Sound production was monitored for sixty hours during the six days she was kept alive. Click trains similar to those reported for adult Dall’s porpoises and other porpoise species were recorded. These clicks consisted of a weak low frequency component which sounded like purring, and a strong, ultrasonic component. Clicks contained energy from 100 to over 200 kHz, with a peak typically near 128 kHz. In one click train, the interval between clicks was measured and found to be relatively constant at about 7.4 msec (corresponding to 135 clicks per second). These observations suggest that the ability to produce clicks develops more rapidly in this porpoise species than in the bottlenose dolphin.
The structure of these clicks was similar to that expected from an adult. This suggests that the ability to produce clicks is fully developed within the first week of life. In contrast, Reiss (in press) found a four week period was required for the development of clicks in two bottlenose dolphins. Phocoenoides calves are born at over 50% of their adult length, which might account for their precocious development. One apparent difference is that doublets as described by Awbrey et al. (1979) have not been found in the click trains from the neonate analyzed to date. Most clicks analyzed to date were probably elicited by stroking her head or back. Mohl and Andersen (1973) elicited clicks from a harbor porpoise in a similar manner. Thus it is unclear whether the clicks were for echolocation or to serve a social function.
Some whistle-like sounds were heard, but these appeared to be associated with the passage of gas in the digestive tract rather than as a form of vocal behavior. Thus these observations are consistent with previous reports of the absence of whistle production by the Phocoenidae.
[Courtesy of the International Marine Animal Trainer’s Association; full paper published with permission.]