The function of multi-pod aggregations of fish-eating killer whales (Orcinus orca) in Kamchatka, Far East Russia

Abstract

In fish-eating North Pacific killer whales, large multi-pod aggregations of up to 100 animals often occur. These aggregations are thought to be reproductive gatherings where mating between members of different pods takes place. However, killer whales are social animals, and the role of these aggregations might also be establishing and maintaining social bonds between pods. Alternatively, it is also possible that multi-pod aggregations are in some way connected with foraging or searching for fish. In this study of killer whales in the western North Pacific, we describe multi-pod aggregations quantitatively and suggest their functional role in the life of fish-eating killer whales. We show that foraging is rare in multi-pod aggregations, whether inter-clan or intra-clan, and thus they are unlikely to play an important role in cooperative foraging. Socialising occurs more frequently in inter-clan rather than in intra-clan aggregations, which suggests the higher arousal level and possible mating during inter-clan aggregations. In summary, multi-pod aggregations of Kamchatka killer whales might be both reproductive assemblages and ''clubs'' of some kind in which whales gather to establish and maintain social bonds.

The social organization of resident-type killer whales (Orcinus orca) in Avacha Gulf, Northwest Pacific, as revealed through association patterns and acoustic similarity

“…Thus, killer whale aggregations seemed to be more than a casual form of killer whale association and may be based on extrinsic ecological factors, such as prey distribution. Filatova et al (2008) found that the level of social behaviour increased in large multi-pod killer whale aggregations. The groupings recorded during these aggregations generally travelled in the same direction, often approaching each other and usually making the same activity changes.…”

“…The competition for resources could be one of the explanations for these processes. The foraging behaviour of resident killer whales is often correlated with fission into smaller subgroups and rarely occurs in large multi-pod killer whale aggregations (Hoelzel 1993;Filatova et al 2008). Adult males tend to forage independently and share prey with other killer whales less often than do adult females and subadults (Hoelzel 1993;Ford and Ellis 2006).…”

Call sharing across vocal clans of killer whales: Evidence for vocal imitation?

“…Resident matrilines may travel on their own for days or weeks, but they also frequently travel and interact with other matrilines from the same or different clans in the community, irrespective of the degree of call sharing (Bigg et al 1990, Ford et al 2000). Mating typically takes place between members of different clans (Barrett‐Lennard 2000) and large aggregations are thought to function in a mating context and for establishment and maintenance of social bonds (Matkin et al 1997, Filatova et al 2009). Vocal activity is particularly high in large aggregations (Ford 1989), where matrilines may share few or no calls at all with other groups present.…”

Responses of Kamchatkan fish‐eating killer whales to playbacks of conspecific calls

“…1997, Barrett‐Lennard 2000). In Kamchatkan killer whales, associations between units sometimes do not correspond with either of these predictions (Ivkovich et al 2010) and the overall picture appears to be more complex, for example, some aggregations appear to serve neither for foraging nor for mating, but rather to establish and maintain social bonds (Filatova et al . 2009 b ).…”

“…Second, unrelated matrilines from different clans could form temporary aggregations for mating reasons (Matkin et al 1997, Barrett-Lennard 2000. In Kamchatkan killer whales, associations between units sometimes do not correspond with either of these predictions (Ivkovich et al 2010) and the overall picture appears to be more complex, for example, some aggregations appear to serve neither for foraging nor for mating, but rather to establish and maintain social bonds (Filatova et al 2009b). This could help explain why units from different pods sometimes appear to ignore each other's calls.…”