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Infanticide in a mammal-eating killer whale population; Jared R. Towers, et al., Scientific Reports volume 8, Article number: 4366 (2018) doi:10.1038/s41598-018-22714-x
Topic Started: Mar 24 2018, 02:57 PM (565 Views)
Taipan
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Note, I dont believe this is 'murder', and I think the article shouldnt have used that term to describe animal behaviour.

Whale Murder Was Sexually Motivated, Whale Detectives Say

By Brandon Specktor, Senior Writer | March 23, 2018 02:56pm ET

Scientists have accused a killer whale of murder — and its 46-year-old mother is an accomplice.

Following a violent whale-on-whale clash near Vancouver Island near western Canada, a male orca and his mother were observed capturing another whale's newborn calf by the tail, abducting it for nearly 3 hours and ultimately drowning it deep underwater.

The marine biologists who witnessed the attack called it "the first account of infanticide reported in killer whales" and "the only case committed jointly by an adult male and his mother" ­outside of humans.

In a new paper that reads like a police report (published March 20 in the journal Scientific Reports), the researchers described the grisly incident — and why they think it may have occurred.

The facts of the crime

Early one December morning, marine biologists at a research station called OrcaLab caught wind of the unfolding attack when they picked up some strange whale calls on an underwater microphone. A squad of three scientists went to investigate.

When the researchers arrived at the source of the distressed calls, it was clear an altercation had occurred. They saw a trio of whales (ages 2, 3 and 13 years old) hauling fin at close to 10 mph (17 km/h) toward a nearby group of their family members. One of the younger whales was wounded, bleeding from a bite wound on its left flank and pocked with fresh teeth marks around its body. The trio was seemingly being chased by an adult male orca (about 32 years old) and its mother (about 46 years old).

Posted Image
The violent orca attack occurred near Vancouver Island in Western Canada. OrcaLab researchers followed the conflict for more than five hours.
Credit: Courtesy Scientific Reports

The fleeing three whales soon rejoined the rest of their family, which included the group's mother (age 28) and several other children, including a little white newborn (or "neonate"). The family began swimming westward together. Soon, though, the aggressively pursuing male and its mother caught up to them.

"Erratic movements and splashing suggestive of a predation event were observed," the researchers wrote. The scuffling whales darted in and out of the sea, splashing sprays of water and blood. After a few minutes, it became clear that the newborn calf had not surfaced with its mother.

Soon, the researchers saw the adult male attacker swim by — with the baby whale hanging out of its mouth. "The fluke of the neonate could be seen in his mouth with the body intact trailing underneath his lower jaw," the researchers wrote.

The mother whale chased after the male attacker, who was now bleeding from fresh bite wounds. At one point, the aggressor male's mother joined the fray by throwing her body in front of the newborn's mom, impeding her pursuit.

All told, the male attacker and his mother kept the captured newborn in their possession for more than 3 hours — finally diving with it deep underwater and drowning it.

Why kill a baby whale?
Infanticidal acts are rarely observed in nature, the researchers wrote, but primates, carnivores, rodents and dolphins have all been caught in the act from time to time.

Posted Image
Blood sprays out of the water as a mother orca fights off the violent male trying to capture her newborn calf.
Credit: Courtesy Scientific Reports/ OrcaLab

Scientists don't fully understand the motives behind animal infanticide, but one prominent theory is that males kill off a female's offspring in order to stop her from lactating, making her eligible to mate again more quickly — in other words, the crimes may be sexually motivated.

"In these cases, infanticide not only creates a mating opportunity but can also remove the progeny of a competing male from the gene pool," the researchers wrote.

That hypothesis could explain the adult male whale's motives in this case, but why get its mom involved? According to the OrcaLab researchers, it's not uncommon to see an adult male orca traveling continuously with its mother and cooperating in predation, especially if the mom is beyond reproductive age.

"Post-reproductive female killer whales increase the survival of adult sons by sharing ecological knowledge and prey with them," the researchers wrote. A mother whale might also try to help its son mate, thus ensuring that the mother's lineage continues, the researchers added.

Additional details in this killer whale killing — including theslain newborn's paternal lineage — remain under investigation.

https://www.livescience.com/62107-orca-killer-whale-infanticide-vancouver.html




Journal Reference:
Jared R. Towers, Muriel J. Hallé, Helena K. Symonds, Gary J. Sutton, Alexandra B. Morton, Paul Spong, James P. Borrowman & John K. B. Ford Infanticide in a mammal-eating killer whale population Scientific Reports volume 8, Article number: 4366 (2018) doi:10.1038/s41598-018-22714-x

Abstract
Infanticide can be an extreme result of sexual conflict that drives selection in species in which it occurs. It is a rarely observed behaviour but some evidence for its occurrence in cetaceans exists in three species of dolphin. Here we describe observations of an adult male killer whale (Orcinus orca) and his post-reproductive mother killing a neonate belonging to an unrelated female from the same population in the North Pacific. This is the first account of infanticide reported in killer whales and the only case committed jointly by an adult male and his mother outside of humans. Consistent with findings in other social mammals, we suggest that infanticide is a sexually selected behaviour in killer whales that could provide subsequent mating opportunities for the infanticidal male and thereby provide inclusive fitness benefits for his mother.
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Attached File Infanticide_in_a_mammal_eating_killer_whale_population.pdf (1.79 MB)
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Thalassophoneus
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I find the whole "crime investigation" theme ridiculous.
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