In a scientific first, a mother killer whale and her adult son were observed working together to kill another whale's newborn calf, according to a new study.
On the day of the attack, scientists heard strange whale calls coming from the research station's hydrophones near the Johnstone Strait and went out on the water to see what was going on.
They observed a 28-year-old mother travelling in a group with five of her offspring, one of which appeared to be a newborn whale.
The scientists observed that the baby whale had "fetal folds" and an unerect dorsal fin, which are only visible on whales during the first few days of their life.
The scientists observed that the family group was being followed by a 32-year-old male orca and his 46-year-old mother.
Suddenly, the scientists observed "erratic movements and splashing suggestive of a predation event." Moments later, the adult male whale swam by the research boat holding the baby whale by the tail.
“The baby was hanging out of his mouth,” cetacean researcher and study coauthor Jared Towers told the Washington Post. “I knew right off the bat — I study killer whales pretty intensively — that this was a ‘first of its kind’ kind of observation.”
“We were a bit horrified, but more so I think we were fascinated,” Towers added. “We knew that it was time to just collect as much data as we could to accurately record our observations.”
According to the study, the newborn calf's mother chased after the adult male as he held her calf underwater, and at one point rammed him, “sending blood and water into the air.”
The adult male kept the newborn calf in his mouth as it slowly drowned while his mother helped fend off attacks from the calf's mother.
After approximately 10 minutes, the whales began to calm down, even though the adult male was still holding the baby whale's body in his mouth. "I think it may be because the mother realized the calf was dead, so what was the point of continuing to fight after that?” Towers told the Washington Post.
The scientists theorized that the male orca committed infanticide so that he could mate with the calf's mother, and the older female helped her son so that her lineage could continue.
"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," authors of the study wrote.
Killer whales gestate fetuses for 17–18 months and then nurse their offspring. While nursing, they cannot become pregnant with another calf.
"I think we don’t give a lot of animals enough credit for their ability to plan and think ahead, but I think that’s exactly what was happening here," Towers told National Geographic. "He and his mom both knew that if the baby was removed he might have a chance at breeding."
