University of York in Centre for Whale Research study

They and others worked with the Centre for Whale Research and confirmed earlier findings that whale mums give more support to their sons than daughters.

The study of whales living near North America also found each male calf reduced a mother’s likelihood of successful further breeding (a calf surviving to one year old) by about half. 

Killer whales mostly eat salmon and the mums would share their fish with their sons until the male reached adulthood, compared to reproductive age for their daughters.

The strategy discovered by this study – in which mothers indefinitely sacrifice their future reproduction to keep their sons alive – is highly unusual in nature and may even be unique. 

Professor Dan Franks, from the Departments of Biology and Computer Science, said: “This strategy of indefinitely sacrificing future reproduction to keep their sons alive may have been beneficial in their evolutionary past, but it now potentially threatens the future viability of the southern resident killer whale population, which is critically endangered with just 73 individuals remaining.”