Scientists at the Whale Research Center discovered that female killer whales continue to care for their adult sons, sacrificing further reproduction. The study was published in the journal Current Biology.
The researchers examined the relationship between 73 mother-cub pairs among killer whales living in waters off the coast of Washington state and British Columbia. It was previously known that both sons and daughters of female killer whales remain in the mother’s population for life. Scientists have found that the female forms a stronger bond with her sons in doing this, helping them hunt and share prey with them. Daughters become completely independent at the age of 6 to 10 years.
Scientists suggest that killer whales have several reasons for their preference. First, males are more difficult to hunt due to their large size and less maneuverability. Second, if the female’s daughter stays in the original population and gives birth, her children will also remain in that population. This means that another mouth will appear in the group to compete with the other offspring of the female matriarch.
In this case, males can also breed while in the maternal population, but their offspring will be in another group. It turns out that the female matriarch wins: her genes have spread, but there is no need to feed her grandchildren.
Interestingly, the female’s own reproductive chances are falling: each adult son reduces the mother’s chances of giving birth to a new offspring by more than 50% per year.