A comparison of the discrete call repertoires of Northeast Atlantic killer whales (Orcinus orca)

• Main Author: Duc, Anne-Valérie
• Format: Bachelor Thesis
• Language: English
• Published: Uppsala universitet, Institutionen för biologisk grundutbildning 2011
• Subjects: killer whale; acoustic; call repertoire; call comparison; Norway; Iceland; Killer Whale; Northeast Atlantic; Orca; Orcinus orca; Killer whale
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-157829

Although Icelandic and Norwegian killer whales are thought to have been in contact prior to the collapse of the herring stock in the 1960s, the Northeast Atlantic killer whales currently seem to show high site fidelity. So far, photoidentification data have suggested movement of a few individuals between East Iceland and North Scotland, and two calls have been shown to be shared by the Icelandic and Norwegian populations. Based on previous and newly analysed call samples, the aim of this study was to describe the geographic variation in the vocal repertoire of the Northeast Atlantic killer whales. Recordings have been conducted off Southwest Iceland in the summers 2004, 2008 and 2009 using sound recording tags attached using suction cups (Dtags), a 4-element vertical hydrophone array and a 2-element towed hydrophone array. From the 57 hours of recording analysed, 1742 calls were classified. In total, 56 distinct call categories composed of 35 call types and 31 subtypes were identified. This discrete call repertoire contained less biphonic calls but more calls composed of buzzes and/or clicks than the Norwegian repertoire. The reasons for these differences remain unknown. One Icelandic call subtype was defined as a compound call, a type of call that is common in the Norwegian population. The comparison of the different vocal repertoires of Northeast Atlantic showed four good or likely call matches in herring-eating killer whales (one between Southwest Iceland and Shetland, one between East Iceland and Norway, and two between Shetland and Norway). No matches were found between Southwest Iceland and East Iceland. I suggest that the four shared calls are most likely to have come from a common ancestral pod and have been transmitted through vocal learning. Over time, geographic isolation of the groups induced by changes in the migratory patterns of the herring might have been accompanied by divergence in their call repertoires.