Ethology and Behavioral Ecology of Odontocetes by Bernd Würsig

Author:Bernd Würsig
Language: eng
Format: epub, pdf
ISBN: 9783030166632
Publisher: Springer International Publishing

11.4 Social Organization

Like most delphinids , killer whales are highly social animals, typically living in groups of a few individuals to 20 or more. However, in contrast to the considerable social fluidity of many coastal dolphin species (Connor et al. 2000), killer whale groups are often highly stable and cohesive over time. In most areas where killer whales have been studied for long periods using individual photographic identification, their primary social units consist of strongly bonded kin related by matrilineal descent (Bigg et al. 1990; Ford and Ellis 1999; Similä and Ugarte 1999; Iñíguez et al. 2005; Tosh et al. 2008; Tixier et al. 2014). Temporal persistence of these bonds is a primary variable determining group sizes and structure in different ecotypes .

The best known society is that of Resident killer whales , which have been studied continuously for over 45 years in coastal British Columbia and Washington State (Bigg et al. 1990; Ford et al. 2000; Towers et al. 2015) and for over 30 years in southern Alaska (Matkin et al. 2014). Long-term studies have also been conducted on Resident-type killer whales off the east coast of Kamchatka (Ivkovich et al. 2010). Resident killer whales live in complex societies based on matrilineal genealogy , social association , and patterns of vocalizations. The basic social unit —the matriline —is a highly stable kin group that consists of a matriarch, her sons and daughters, and the daughters’ offspring. Because the lifespan of females can reach 80 years and females have their first calf at 12–14 years (Olesiuk et al. 2005), matrilines may contain four and occasionally five generations of maternally related individuals. Remarkably, both males and females stay with their close kin for life—no individual whales have been observed to leave their matriline and join another on a long-term basis. Lifetime natal philopatry with the complete absence of dispersal is exceedingly rare in mammals (Wright et al. 2016). As a result, the matrilines of Resident killer whales are perhaps the most enduring social groupings of any mammal (Fig. 11.1).

Fig. 11.1A matrilineal group of Resident killer whales , Orcinus orca, with three generations. Shown is the ca. 63-year-old matriarch A30 at left in the image, in the back, her ca. 41-year-old son A38 to her left, and her 27-year-old daughter A50 to his left. A50’s two young offspring, A84 (6 years old, at the rear) and A99 (newborn , surfacing), swim alongside their mother. Photo by Jared Towers

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