Back to the Black
The Release of Dicky in the Black Sea, after spending six years in the Red Sea.- And his vocalizations during different stages of arousal -
VOCAL BEHAVIOUR OF DICKY
Whistle vocalizations during periods of high arousal
During the ten hours of transport from Israel to Russia, the vocal behaviour of Dicky was very variable. Periods of silence changed with periods of high vocal activity, the latter often accompanied with erratic body movements. Transitions between these two states could be sudden, but more typical were intermediate levels, both regarding the rate of vocalizations and the intensity of body movements. The most dramatic increases in the vocalization rate occurred immediately following pertubations of the environmental situation, especially when it constituted a novel situation, like lifting with a stretcher or the starting of an engine. Then, up to 50 whistle-loops per minute were produced by Dicky, with loops referring to repetitive elements within a continuous whistle vocalization. Such repetitive elements were common during this context, with a maximum of 14 uninterrupted loops.
The majority of whistles during these highly active states were of relative stereotyped contour. This type was accepted as Dicky's signature whistle (Caldwell & Caldwell 1965, 1968). We assume that this state of high activity, together with the production of a stereotyped whistle contour, indicated a high degree of distress (see also Sidorova et al. 1990). A striking feature of vocalizations during the transport was a high proportion of whistles uttered simultaneously with clicks. The clicks gave the sound a specific acoustic character that was clearly different from pure whistle vocalizations. In some samples, these whistle/click combinations constituted more than 40% of whistles. Clicks were typically emitted during the part of the whistle that was rising in frequency, with a mean rate of about 110 clicks per second. In the time domain, these whistles were typically shortened when compared with pure whistles of the same contour. Comparing with contexts in which we could record such sound types from the dolphin group in Eilat, like play-chases or passing novel structures with high speed, we assume that whistle/click combinations indicate a more general state of excitement.
Whistle vocalizations during periods of lower arousal
The whistles Dicky produced during intermediate levels of arousal, regarding body movements and whistle frequency, were of different types. Some showed a remarkable variability, which not always allowed for an unequivocal categorization. His signature whistle still occurred, but was not as prevailing as during states of higher arousal. If only these periods would have been analysed, we would have not been able to assign a stereotyped and individual-specific contour to Dicky. Thus, his vocal behaviour only partially followed the predictions of the signature whistle hypothesis (Caldwell et al. 1990). His whistling behaviour in situations of separation in general does not allow for an identification of his signature whistle. It might explain our inability to do this prior to his transport, as opposed to all other dolphins of the Dolphin Reef group. Comparable vocal behaviours were reported for two other bottlenose dolphins recorded during different stages of habituation to stress-inducing contexts (Sidorova et al. 1990).
Other whistle types produced by Dicky during lower levels of arousal, and that could be categorized unambiguously, were known from the repertoire of the group at Dolphin Reef. They included, for example, types we refer to as ‘Hook’ and ‘D-whistle’. But most surprising was Dicky’s production of signature whistles of his group mates while being isolated in the transportation tank. He emitted several signature whistles of the adult male Cindy, the adult female Shy, and the female calf Nana. Bottlenose dolphins were reported to imitate each others signature whistles during direct social interaction (Tyack 1986), or while acoustically connected via an electronic channel (Burdin et al. 1975), and it was suggested that this might function in addressing a specific social partner. But to our knowledge this is the first report on the use of signature whistles of other group members in total isolation from other dolphins.
Shortly after Dicky was introduced into the open sea pen at the Black Sea, where he joined the female (with six other bottlenose dolphins in adjacent pens), we could record the signature whistles of other members from the Dolphin Reef group (again of Cindy, Shy, and Nana, and additionally of Pashosh, a juvenile female). Although I was not able to identify the sender of these whistles in the given situation, they were very probably produced by Dicky. It could be speculated that one of the present dolphins hypothetically associated Dicky with Cindy and Shy, as all three belonged to the original group captured from that population, but both Pashosh and Nana were only born at Dolphin Reef in Eilat. Thus, we can state that Dicky’s imitations of signature whistles occurred again without vocal contact to the respective animals.
Frequency spectrograms of signature whistle imitations of
About 48 hours later Dicky and the female were transferred to a pool, where they stayed the last night before their transport to the release site. Just before they were set into the pool, both animals were marked on their dorsal fin (see above), and both showed signs of high distress during this manipulation. Dicky only produced his signature whistle, and also the female produced a highly stereotyped contour, which was accepted as her signature whistle.
We consider five factors as having been particularly important for the success of this project. (1) The individual: With an estimated age of eleven years, Dicky was a young, wild-born, sexually mature male. (2) The housing conditions in the Dolphin Reef Eilat: The open sea enclosure allowed for example the catching of fish within the site. An 'open-sea-program' gave Dicky access to the open sea on a daily base for the last year. (3) Release at the site of capture: This method is preferable for reasons of population genetics as well as the adaptiveness of the animal to its original environment. (4) Release together with a 'wild' conspecific: Upon arrival at the Black Sea, Dicky was allowed to accustom to the new site by spending three days in an open sea pen, in which a conspecific female was kept, too. (5) No use of artificial tracking devices: Such a device might affect the behaviour of its carrier and that of its potential social partners. Against the original plan of attaching satellite tags it was therefore decided to mark the two dolphins at their dorsal fins and to conduct systematic surveys of their potential range, including Taman Bay and the Russian/Ukrainian coast of the Black Sea, as well as informing fisherman and sailor of the area. Several re-sightings over a period of four years post-release confirmed the success of this unique release project.