Yahoo News Killer whale mothers make 'lifelong sacrifices' while raising sons
Orca mothers make "lifelong sacrifices" for their sons, a new study has revealed.
Female killer whales continue to nurture their off-spring at the bitter cost of their own reproductive system.
The study carried out by the universities of Exeter, York and Cambridge, and the Centre for Whale Research (CWR) suggested that maternal presence enhances the survival rates - particularly for males.
Biologists used data from 1982 to 2021 on 40 females in the "southern resident" killer whale population, which live off the Pacific coast of North America.
Dr Michael Weiss, of the Centre for Research in Animal Behaviour at the University of Exeter, said: "Our previous research has shown that sons have a higher chance of survival if their mother is around".
But, he added, their maternal instincts came at a price, "In terms of their future reproduction to keep their sons alive".
Male and female resident killer whales stay in the groups they were born into and each group is led by an experienced female.
The southern resident orcas are fish-eating whales and feed predominantly on salmon.
The mothers bite the salmon in two, eating one half and giving the other to their sons.
The daughters are fed till a certain age, but once they reach their reproductive years - they are no longer looked after.
"Mothers pay more attention to their sons than their daughters, particularly once females achieve adulthood," researchers from CWR said.
Professor Darren Croft, Professor of Animal Behaviour at the University of Exeter, said mothers gain an "indirect fitness" benefit when their sons are taken care of.
It is believed to improve chances of their genes passing onto future generations.
The reasons as to why this may effect the female whales' reproductive process has not yet been figured out.
The researchers in the CWR journal said they think the pattern is "part driven by the costs of provisioning sons through directed prey sharing".
In order for a female to be able to reproduce, they need food to sustain themselves, "and thus reductions in food intake due to prey sharing are likely to have significant impacts".
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The southern killer whales have been decline since the early 1990s, according to biologists in the CWR journal.
Chinook salmon is often eaten by these mammals in order to survive.
However, the number of these fishes has now declined - with many stocks threatened or endangered.
Professor Croft said: "For this population that's living on a knife's edge, the potential for population recovery is going to be limited by the number of females and those females' reproductive output.
"A strategy of females reducing reproduction to increase the survival of male offspring may therefore have negative impacts on this population's recovery."
