Vocal repertoires of two matrilineal social whale species Long-finned Pilot whales (Globicephala melas) & Killer whales (Orcinus orca) in northern Norway

Abstract

The aim of this study was to describe and investigate the vocal repertoire and possible factors influencing the size and composition of two matrilineal social whale species: long-finned pilot whales and killer whales in Norway. I was not able to describe the entire vocal repertoire due to the large number of animals in this population and the limitations of fieldwork and time. In this thesis I describe a vocal repertoire subset from seven groups of pilot whales and 11 groups of killer whales recorded in the Vestfjord in northern Norway during the time period 2004 until 2011. Using observer-based acoustic analysis I could discern 129 call types and 25 subtypes for long-finned pilot whales, and 60 call types and 25 subtypes for killer whales. Per group, pilot whales used an average of 36 call types and killer whales just 25. The general structure of call types was similar, with most call types consisting of one segment and two elements with different structures. The main element structure in pilot whale and killer whale calls was an ascending frequency band. The amount of two-voiced calls was 29% for pilot whales and 47% for killer whales. In addition, I further found different call type combinations and repetitions and investigated ultrasonic whistles, already known in killer whales, but newly described for pilot whales in this study. The main difference between vocal repertoires of the two species appeared when I looked at call type sharing between the recorded groups. Here I found that pilot whales only shared 28% of their call types and 37% of their total calls with at least one other group, whereas killer whales shared 59% of their call types and 90% of their total calls. Average group size differed: pilot whales were found in larger groups (23 animals) than killer whales (9 animals). Overall number of calls increases with group size, however, I could not find that group size influenced the number of call types. I found rather that vocal repertoire size depends on the length of recording time and of a group’s vocal activity. This must be over one hour at minimum before it can be compared with another. During carousel feeding in killer whales, vocal activity increased. This indicates that behaviour does play a role in vocal repertoire size and composition, at least in killer whales where behaviour is easier to detect and measure than in pilot whales. In 2011 I discovered a new foraging method for salmon by killer whales in Norway. The publication is presented in Chapter 6. For the first time I was able to observe the same two groups of killer whales for over three months and describe a full repertoire with 59 call types and 25 subtypes. It was not possible to separate the calling of the two groups, but nevertheless it shows that the vocal repertoire is larger than for my earlier, shorter observations. In addition, I found context-specific vocalisations during salmon feeding and non-feeding, and compared it to herring feeding and a food association call from the Icelandic killer whale population. Specifically, certain call type combinations contained the same beginning part (call type NKW-15) in all feeding contexts, but the combinations differed for salmon and herring feeding and between groups. I discuss the possibility of referential and arousal calling in association with food in killer whales. This thesis is summarised in Chapter 8 with a discussion of all presented results, the limitations of the research, and potential areas for further study to increase our understanding of the two species and study vocal communication more generally in cetaceans.