Orcas are attacking boats. But is it revenge or trauma?

Orcas may be one of the ocean’s top predators, but they’ve rarely shown aggression against humans or watercraft in the past. But since 2020, orca pods have increasingly targeted sailboats off the Iberian Peninsula in Western Europe. In one instance, three of the black and white whales destroyed a vessel’s rudder, causing it to sink before it reached port. The Spanish coast guard called in a helicopter and sea cruiser to rescue the sailors.

The sea-mammal strikes have left scientists, sailors and social media users contemplating what’s changed in the last few years to cause this shift in behavior. Some experts suspect that one of the older female orcas involved, named White Gladis, had previously been hit by a ship or entrapped during illegal fishing. Questions arose. Are the whales attacking the boats to avenge White Gladis? Or are they simply defending themselves against more possible harm? Maybe they’re just playing with the sailboats? If the attacks were vengeful or defensive, does that mean orcas, and animals in general, can share their traumas with their social groups?

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Wild orcas don’t attack humans or approach boats. The subpopulation off the Iberian coast is considered critically endangered with only up to 50 adults, according to a 2019 estimate from the International Union for Conservation of Nature. But authorities worry that the number of attacks means they will continue. The Atlantic Orca Working group told The New York Times that since 2020, orcas were documented swimming at or reacting to vessels about 500 times in the seas around Morocco, Portugal, and Spain. They caused physical damage to the watercraft in about a fifth of those incidents.

Whether the attacks were motivated by vengeance, defense, or play is up for debate. David Diamond, a psychology professor at the University of South Florida, who studies how stress affects the brain in humans and animals, says it’s important to remember that we never know what an animal is thinking. “We interpret what they’re thinking from their behavior.”

Some scientists who study orcas suggested the strikes were playful given the species’ mischievous nature. Diamond, on the other hand, believes the animals are capable of retribution. He often shows videos of orcas in class and notes how they have a mammalian brain that is functionally similar to humans. “I can actually see the killer whale taking a proactive approach to say, this thing on the surface caused me harm so I want to get all my hunting party together and attack it,” he explains.

Linking the orca attacks to post-traumatic stress disorder, though, could be taking it too far. While White Gladis might have had a negative experience with a boat, it’s unlikely that she suffers from PTSD as some have speculated. The condition is unique to humans as it is diagnosed through self reports and not any physical test, Diamond says. More importantly, its symptoms go deeper than just remembering a harrowing experience and being fearful of it. “It changes [a person’s] personality; it changes their life,” he says. “So we don’t want to trivialize PTSD by saying, this orca had a terrible experience, therefore it has PTSD. Most people have terrible experiences in their lives and don’t develop PTSD.”

Even if animals don’t fit the clinical definition of PTSD patients, they could remember traumatic experiences or develop PTSD-like effects. In one study, Diamond’s team put lab rats in a box with cats, their natural predator. It triggered a part of the rodents’ brains known to be connected to the fear of death. Many weeks later, researchers put the rats back in the box in a different room without similar scents or cats. The subjects showed tremendous unease with the box itself, Diamond says. In another experiment, he paired a different set of rats and cats in boxes multiple times, and then sent the rodents to live with an unfamiliar rat afterward to simulate an unstable social life. They started to produce PTSD-like effects with changes in their physiology and behavior.

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And what about their roommates, or in the orcas’ case, their pod mates? It’s unlikely that animals can rehash all the details of a traumatic event to their acquaintances, but they might still be able to tip them off to the source of the trauma—and the subsequent dangers. About 16 years ago, John Marzluff, a professor of wildlife science at the University of Washington, captured American crows using nets to tag them with colored leg bands, so he could follow their behavior over their lifetimes. Now, many crows in the same neck of the woods show hostile behavior to humans. A lot of the birds that weren’t tagged “respond to us like we caught them,” Marzluff says. “So they are learning that we’re dangerous from others that either experienced it or saw the initial capture.”

Crows don’t just use group interactions to warn each other: They might take advantage of their numbers to engage with the threat. When the corvids see something they think is dangerous, they let out a harsh, scolding sound. Other crows hear it and then join in. “So it’s not like they’re telling one another, ‘Hey, there’s this guy who comes around once a year, watch out for him,’” Marzluff says. “It’s like, ‘I see this thing, which I’ve heard or known to be dangerous, come in here and learn about it with me. So from the orca example, it seems like they might be doing similar things.”

In another example, elephant mothers in Gorongosa National Park who survived hunters during Mozambique’s civil war sometimes enlist their kin and clans to chase away humans who come near them. It’s a defensive action, according to Liana Zanette, a biology professor at the University of Western Ontario, who researches predator-prey interactions. “These females lived during this time of this brutality by humans,” she says. “And so now whenever they see a human, they recognize it as a significant threat.”

While we may never fully never know why animals act the way they do, one thing is certain: Our presence makes a difference. Whether it’s an orca in the Strait of Gibraltar or a bird in your backyard, Marzluff says that we should know that animals are paying attention to what we do. “They do take information about our activities and use it in their behavior later,” he says. “We’re not just this static part of their environment. We’re an active species that they take seriously and respond to.”