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The function of stereotyped calls of killer whales: a comparative approach

Final Activity Report Summary - FSVKW:ACA (The Function of Stereotyped Calls of Killer Whales: A Comparative Approach)

The objectives of the project were:

1. to describe the vocal behaviour of Scottish killer whales
2. to measure the loudness of killer whale vocalisations
3. to conduct playback experiments to test whether killer whales discriminated between familiar and unfamiliar calls and
4. to use playback to test the response of killer whales to food-related sounds.

The description of the vocal behaviour was entirely successful. Field recordings were made off Shetland in 2008 and 2009 and archival recordings were obtained from the Scottish west coast. The results of the analysis showed that groups with different vocal repertoires were found in Shetland waters and that these groups appeared to specialise on different prey, i.e. on sea mammals and fish respectively. No call types were shared between Shetland and the west coast of Scotland.

Measurements of loudness of killer whale calls were also successfully made using archival data from British Columbia and Shetland killer whales. The results showed significant differences in call loudness between populations feeding on sea mammals and those feeding on fish. This suggested that, in addition to reducing vocal behaviour altogether, mammal-hunting killer whales also reduced the loudness of their calls, presumably to avoid detection by their acoustically sensitive prey.

A playback trial was conducted to test the response of killer whales to conspecific calls. The response of the focal group exceeded the one deemed acceptable by the research permit, so that only one playback was conducted. However, since the focal group contained an individual equipped with a tag recording its underwater movements and any sounds it made or heard, the single trial provided much valuable information about the response to conspecific calls. It also showed that playback could be a useful management tool to modify the behaviour of killer whales. Playbacks of food-related sounds were conducted in Icelandic waters. The responses to playbacks were ambiguous and did not a reveal a distinctive approach or avoidance of the playback source.

The fellow developed additional lines of research into the strategies employed by fish-eating killer whales to detect and catch large individual fish, based on British Columbia residents, and schooling prey, based on north Atlantic herring eating killer whales, as well as into the vocal behaviour associated with prey sharing in British Columbia residents. He also developed new collaborations with European and international researchers and gained valuable experience conducting field research in European waters. During his time at the ‘Sea Mammal Research Unit’, the fellow received training in methods of sound localisation, measurements of source levels, use of digital recording tags and on conducting playback experiments. The fellow published one scientific paper during the fellowship period and at least an additional four publications were anticipated to result from the project. He attended and presented his results at two conferences and two workshops and the project received considerable media attention, both in Scotland and internationally.