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Friday, March 23, 2018

Killer Whale "Infanticide Teamwork"

"Intense vocal activity could be heard."
"It was not the kind of thing you can un-see, the image of the whales killing and passing around the dead baby are engraved in my mind."
"It's horrifying and fascinating at the same time."
Jared Towers, cetacean ecologist, Pacific Biological Station, Nanaimo, British Columbia

"Although killer whales [Orcinus orca] are one of the most studied and widespread species of cetacean, only a few observations of aggression between individuals of the same population have been reported."
"A secondary benefit of some infanticide events best explained by the sexual selection hypothesis [is the meal resulting from the kill]."
B.C. cetacean scientists' report
Transient killer whale infanticide
The male killer whale holds the calf in its mouth. (Gary Sutton)
Nature's evolutionary formula is not always pretty. Her creatures have been programmed to use some fairly ghastly, viciously violent means of ensuring their survival. Genetic survival is the cause of primal imprinted behaviours that express themselves in many species, and humankind is not exempt.
Our propensity as individuals and as groups, to view one another with suspicion is readily translated into hatred, an emotion often leading to threats and violence. The territorial imperative is, of course, inextricably linked to survival.

So it was at the beginning of time, so it is at the present time for humankind. And for other beasts that nature has contrived to live on this Earth that we share. Recently orca researchers at the northwest end of Vancouver Island came across an event never before catalogued as having been witnessed. An adult killer male committing infanticide in the company of its mother. The mother, at 50 years of age herself beyond conception, the son at 38, carrying her genetic history in search of a mate. Together they indulged in what the observing scientists coined as "infanticidal teamwork".

It has been known to biologists specializing in cetacean ecology that older female killer whales take a hand in assisting their male offspring to acquire mates. What has hitherto not been known that in so doing they may also help to kill the newborns of female orcas they mean to themselves impregnate. On December 2, 2016, close to Ledge Point located between Malcolm Island and Vancouver Island, scientists of the Nanaimo Pacific Biological Station witnessed just such an event.
Transient killer whale infanticide map
A map shows the location of the attack. (Jared Towers)

They saw an nauseating event unfold before their eyes as a 38-year-old adult male and his 50-year-old mother chased a 13-year-old orca mother, her three-year-old sister and the 13-year-old's newborn. Bite wounds could be seen on the bleeding sister orca. The male and his mother caught up to the desperately fleeing younger orcas and the scientists realized they were witness to a "predation event", and before long the newborn was no longer swimming.

They watched, incredulous, as the adult male swam about, the newborn in its mouth, its mother chasing the mature male as it was in the process of drowning it. A few minutes on the infant orca was dead, the killer and his mother swam off with the newborn, exchanging it from time to time so each swam about with it throughout the afternoon hours, followed by the mother and her sister. Light faded into dusk and the sun went down and the mother and son still celebrated their kill.

Conspecific infanticide, where newborns of the same species are killed is considered to be rare, but among primates, carnivores and rodents it does happen. Orcas are generally known to be peaceful creatures. On the other hand, there is ample documentation that many males and females of all age groups bear the teeth marks of other killer whales on their bodies. One possible explanation for an event that puzzles scientists is the male that kills an infant speeds up the new mother's fertility.

The male that has killed a newborn is indulging his own evolutionary role in passing his genes forward down the generations. In killing the infant his own procreation odds have been increased; as lactation stops in the recently bereaved orca mother and estrus resumes, the killer orca can then impregnate the female, bypassing the wait time for the calf he has killed to be weaned. Future competition his own offspring may face has been disposed of, additionally.

Clockwise from top left: wounds on a young female, mother and newborn flee an adult male and his mother, they are caught, blood sprays as the newborn is killed.  Scientific Reports

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