Killer whale moms may be feeding their sons into extinction

A specific species of male orca whales live in a state of perpetual adolescence, to everyone's potential detriment.

Man-child, mama's boy, adult child — if you know the type, you know.

Cooking anything beyond an egg ends in disaster. And they still receive a steady allowance from their parents … at age 35. Wholly dependent on their mothers, they are stuck in perpetual adolescence. They may have grown to rely on it or struggle to achieve independence — families can be complicated — but either way, such relationships can be bad for the whole community.

While humans are lucky this behavior is more the exception and less the rule, it's the other way around for male orca whales, who, according to a paper published in Current Biology on February 8, remain big babies their entire lives.

That occurs to the detriment of their mothers, who, by devoting all their time, resources and energy to their demanding sons, abstain from further reproduction.

It is a pattern that could explain the decreased reproductive output of the critically endangered species, the researchers write in the paper.

Orca moms fully invest themselves in male offspring

The study took place over nearly half a century and followed the lives of 40 female orca whales. The researchers wanted to understand why the species was becoming increasingly endangered.

They found that when female orca whales had sons their chances of giving birth to future offspring reduced by 50%. This remained the case throughout the mother's lifetime and was not observed in orcas who gave birth to daughters.

"Killer whale mothers pay a high cost in terms of their future reproduction to keep their sons alive," said researcher and co-author of the study, Michael Weiss, in a statement. 

Weiss is based at the Centre for Research in Animal Behaviour at the University of Exeter. He and his colleagues used data from a "southern resident" orca whale population, which generally live off the coasts of British Columbia and the US states of Washington and Oregon.

The southern resident species of orca whales has been endangered since 2005.

Unlike other types of killer whales, members of this population subsist almost entirely on Chinook salmon, many species of which are considered threatened or endangered themselves.

As such, there is a lack of food for the whales and that is contributing to the dwindling numbers of the southern resident orca population, which totals only 73 whales at time of writing.

Close mother-son relationship

It was along with these findings about the decreased reproduction rates that the researchers also noted how orca mothers continued a very close maternal relationship with their male offspring. The mothers gave their sons half the salmon they caught for themselves, for example.

That was not the case for the orca daughters, who were generally fed by their mothers until they reached their own reproductive age.

There is an idea that this behavior — to ensure the young male ocas are fed and fit — could be an attempt by their mothers to increase the overall reproductive output of their population. Healthy males mate with many females, and that ultimately could increase the number of future offspring.

But the researchers say that given the critical state of the orca population, the tactic looks like it is having the opposite effect.

"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," said Dan Franks, a professor of biology and computer science at the University of York in a statement.