Bigg’s killer whale females maintain close relationships with their adult sons, while daughters disperse
Post-reproductive mother T60 and her adult son T60C.
(Photograph © Copyright 2023 Center for Whale Research).
Drawing upon an impressive dataset spanning nearly half a century of observations collected on Bigg’s killer whales by CWR, DFO, Bay Cetology, and numerous other Canadian and American organizations, researchers explored how the social bond between mother and offspring change with age and sex of the offspring.
In a new study led by the Center for Whale Research (CWR), Fisheries and Oceans Canada (DFO), and the University of Exeter, Temporal dynamics of mother-offspring relationships in Bigg’s killer whales: opportunities for kin-directed help by post-reproductive females, researchers provide new insight into the social relationships of the mammal-eating Bigg’s (Transient) killer whale. The research team also included the University of York and Bay Cetology, with partial funding from the Natural Environment Research Council (NERC).
In previous research, we have shown that female Biggs killer whales go through menopause at a similar age to the Southern Resident killer whales (SRKW). Prolonged life after reproduction (post-reproductive life) is thought to have evolved due to the benefits that post-reproductive females can gain by helping their offspring and grand offspring (their kin) survive and reproduce. In the SRKWs, both sons and daughters stay in their mother’s group, and our previous research has shown that post-reproductive females increase the survival of their offspring and grand offspring, particularly their adult sons. It is known from early work that Bigg’s and the SRKWs have a different social structure. What was unclear is if post-reproductive mothers have the opportunity to provide help to their offspring and grand offspring in a similar way to what we see in the SRKWs.
Drawing upon an impressive dataset spanning nearly half a century of observations collected on Bigg’s killer whales by CWR, DFO, Bay Cetology, and numerous other Canadian and American organizations, researchers explored how the social bond between mother and offspring change with age and sex of the offspring.
Including associations of 390 unique pairs of females and their offspring, this research shows that the dynamic changes of mother-offspring relationships depend on whether the offspring is male or female. While both sons and daughters will be in a strong relationship with their mother from birth, and while juvenile, the bond between a mother and her daughter will weaken as the daughter reaches reproductive age. This suggests that daughters are likely to disperse as they have had at least their first offspring, budding off from their mother’s group to establish their own family group. Sons, on the other hand, are likely to maintain a strong bond with their mother beyond physical maturity and potentially for life.
Although the benefits of these long-lasting mother-son relationships remain unknown, they could provide the opportunity for females to support their sons either through sharing knowledge or resources or passing on important social connections—benefits that could help explain the presence of menopause in this killer whale ecotype. Current research by the Center for Whale Research, in partnership with the University of Exeter, is using video collected from an unpiloted aerial vehicle (i.e., drone) to examine how post-reproductive females help and support their family group. We hope to be able to provide an update on this research in the near future.
Including associations of 390 unique pairs of females and their offspring, this research shows that the dynamic changes of mother-offspring relationships depend on whether the offspring is male or female.
Post-reproductive mother T100 traveling with her adult son T100C and daughter T100E.
(Photograph © Copyright 2023 Center for Whale Research).
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