‘HORRIFYING AND FASCINATING’ AT THE SAME TIME
SEXUAL SELECTION AT ITS UGLIEST: SCIENTISTS IN B.C. OBSERVE FIRST WHALE INFANTICIDE
following on the recent news that male red squirrels engage in the murder of their rivals’ offspring in order to steal their mates, canadian researchers have found a parallel in killer whales that suggests this massacre of innocents is encouraged by evolution as a winning strategy for males on the make.
by a stroke of luck, orca researchers at the northwest end of vancouver island witnessed an adult male commit the first whale infanticide known to science.
even worse, the killer’s mother, past her own reproductive years, helped her son bite, crush and drown the poor newborn, just a few days after its birth to an unrelated female.
there is already good evidence that older female killer whales help their sons acquire mates, but doing so by killing their love interests’ newborns is novel. this “infanticidal teamwork,” as a new scientific report calls it, seems all very shakespearean, but it is not entirely surprising.
it all went down just after noon on dec. 2, 2016, near ledge point, between malcolm island and vancouver island. when cetacean ecologist jared towers and colleagues of the pacific biological station in nanaimo picked up unusual noises, they saw that a 38-year-old adult male and his nearly 50-year-old mother were chasing a 13-year-old mother, her newborn offspring and her three-year-old sister.
the sister had visible bite wounds and a kink in her fin, and was bleeding. after the male and his mother caught them, with all the thrashing and splashing of what the researchers call a “predation event,” the team noticed the newborn was no longer surfacing.
there followed what is likely the most brutal and ugly scene ever witnessed by cetacean scientists — the adult male was swimming around with the newborn’s tail in its mouth, being chased by the mother. he was drowning it.
“intense vocal activity could be heard,” the team writes in the journal scientific reports.
“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,” towers told the columbia valley pioneer. “it’s horrifying and fascinating at the same time.”
it was all over a few minutes later, and the killer son and mother swam away with the newborn, each holding it at different times, trailed slowly through the afternoon by the mother and her sister.
the researchers followed them until light faded, more than three hours in all, hoping to recover the body, but mother and son still had it as the sun went down. there was no evidence that they ate it, such as a slick on the surface or the attention of scavenger birds, although they cannot be sure.
killing newborns of one’s own species, known as conspecific infanticide, is rare among mammals, but it happens, mostly among primates, carnivores and rodents, and possibly dolphins. but it can be hard to tease out cause from effect when these events are so rarely observed.
the motivation is mysterious. are they doing it for cannibalism, or for sport, or because of stress, or some kind of orca mental illness? it is particularly strange because orcas are generally so nice to each other. as the authors put it, “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.”
menacingly, however, it is well documented that many individuals, males and females of all ages, have the teeth marks of other killer whales in their flesh.
so something wicked is going on under the surface of the ocean. but killing an infant seems particularly nasty, a crime of a different order than two adults fighting.
one key explanation is evolutionary, that a male who kills an infant also makes its mother fertile again. so in effect, the infanticidal male has done three useful things for his odds of passing his own genes, and their role in this murderous behaviour, down the generations.
first, he boosts his own odds of procreating, and can do it in as little as a couple of months with the infant’s mother, as lactation stops and estrus resumes, rather than waiting far longer for the calf to wean.
second, he gets rid of future competition for his own offspring.
lastly, of course, he has made himself a tasty meal, which the authors coldly describe as a “secondary benefit of some infanticide events best explained by the sexual selection hypothesis.”
what is most striking in this b.c. case is the role of the accomplice mother. the theory is that it helps her son’s chances of procreating, which would seem to give the mother an evolutionary advantage too, in that her genes are more likely to live on through him.