Everything we thought we knew about killer whales has been shaken up.
Today, the article “Infanticide in a mammal-eating killer whale population” by Towers et al. was published in the journal Nature. It documents the very first case of infanticide (the killing of an infant) in killer whales. It is also the first case of a mother-assisted infanticide in a species other than humans.
Up until now, aggressive interactions between killer whales (in the wild, at least) were virtually unheard of. Just the other day I was pondering the lack of violence in killer whale society. But just as killer whales tend to do, they upturned everything we thought we knew about them.
The attack involved the T068s and T046Bs, two families of West Coast Transient killer whales.
Post-reproductive female T068 and her son, T068A, attacked mother T046B and her offspring. A previously undocumented neonate, dubbed T046B5, was present, and it became clear that this calf was the target of the attack.
Figure caption from the article: “Observations leading to infanticide. (A) Fresh wounds on left flank and kinked spine anterior to dorsal fin on T046B4. (B) T046B with offspring T046B2 and (neonate) T046B5. (C) T068A surrounded by T046B, T046B1 and T046B1A. (D) T046B ramming T068A from below sending spray and blood into the air.”
T046B attempted to protect her calf by ramming the male T068A. Other members of the T046B family also appeared to try and get the calf back. At one point, T068A had grabbed the neonate by the flukes and likely had drowned it. He paraded the calf’s carcass around in his mouth. Both he and his mother took turns carrying the calf around while the T046Bs trailed behind them. The researchers recording this attack were also using a hydrophone to listen to the whales’ calls, and they documented highly erratic vocalizations that have never been heard before.
Figure caption from the article: “Observations following infanticide. (A) T068A with the fluke of T046B5 in the left side of his mouth. Fresh scars from the teeth of another whale can be seen on his left flank and rostrum. (B) T068 surfacing with the fluke of T046B5 visible in the left side of her mouth. (C) T068A surfacing with the dorsal fin of T046B5 visible off the left side of his melon. (D) T068 rostrum to rostrum with T046B5 approximately 215 minutes after its death.”
Eventually, the light was dim and researchers had to leave the group.
This leaves us all wondering: what is going on? Why did the T068s kill a neonate calf? In other species, infanticide is fairly common as the killing of an infant often brings the mother back into estrus and males can mate with her. It’s likely this is what was going on as other explanations, such as competition for resources, do not adequately explain it.
This is a major discovery in killer whale behavior and I have no doubt we’ll learn more as the years go by.
This is absolutely wild
I just read the article and there are so many interesting tidbits. For instance, I found this really fascinating:
“…T068A, T068 and T046B had only been documented together on two previous occasions – once in 2005 and again in 2007. The apparent low levels of association between these individuals suggest that they are not well known to each other and this may be reflective of inherent sexual conflict between their differing sex and age classes.”
What’s also really interesting (though not necessarily surprising) is that this attack was highly coordinated between T068, a post-menopausal female, and her adult son. The paper essentially concludes that the infanticide was conducted in order to bring T046B back into estrus, and that T068 would serve to benefit by having her son’s genes passed on should he mate with T046B.
Regardless, this is still an incredible discovery. Who knows if this is a somewhat regular occurrence in WCTs (or other orca populations), or if this was an aberrant or unusual encounter…
This is insane!! Is there anywhere to listen to the hydrophone recordings?
If you follow the link to the paper, there are several recordings of the vocalizations as well as some footage (underwater and above water) of the attack in the supplementary material section.
a NRKW made this meme