In 2009, Robert Pitman saw something remarkable. From aboard a research vessel off Antarctica, he watched as a pod of killer whales knocked a seal from an ice floe and closed in for the kill. But before they could, a pair of humpback whales swooped in and rescued the seal, with one of the humpbacks rolling over and lifting the seal out of the water onto its chest, out of harm’s way. Later, when Pitman and the other researchers reviewed film of the event, they were astounded to see just how deliberately the humpback seemed to be protecting the seal.
“In slow motion, you can see the seal starts to slide off, and the humpback takes its 15-foot flipper that weighs about a ton and nudges the seal back onto its chest,” says Pitman, a marine ecologist with the National Oceanic and Atmospheric Administration.
The incident got Pitman thinking — is it really possible humpbacks protect members of other species? Pure altruism is a charged topic among scientists who study the animal kingdom; in a Darwinian world where self-interest rules, it’s hard to figure why a whale would spend time and energy to benefit a seal. But that footage, and two similar interactions Pitman observed on the same voyage, made him think something unexpected might really be going on.
Seven years later, he has a new study in the journal Marine Mammal Science that concludes it is indeed. The paper draws on 115 observed interactions between humpbacks and killer whales — many submitted by “citizen scientists” who saw the interplay from recreational whale-watching boats — and concludes that humpbacks do in fact engage in what Pitman calls “inadvertent altruism” toward marine species like seals, sea lions, ocean sunfish, and even the calves of other whale species being attacked by killer whales.
To understand how this dynamic might emerge, you need to know another side of the relationship between the two whale species: Killer whales love to feast on humpback calves. Humpback calves are born in low latitudes like Hawaii and then travel with their mothers to feeding grounds off California and Alaska. They’ll typically spend the rest of their lives migrating between those two locations, and because they stick to such a regular transit, they’re often in the company of other humpbacks who are genetically related to them. This creates a perfect evolutionary motive for humpbacks to circle the wagons whenever killer whales attack.
“In a feeding area, humpbacks are likely to be related, even distantly related,” says Pitman. “We think this is why humpbacks come in when killer whales are attacking humpback calves. They’ve got a vested interest.”
But why would humpbacks do the same thing for a seal? Pitman thinks it’s because humpbacks err on the side of being overprotective, activating this defense behavior whenever they hear killer whales making hunting vocalizations.
“Humpbacks don’t know what [the killer whales] are preying on,” says Pitman. “Their generalized response when killer whales are attacking is to drive them off. If they were more clever, they’d say this isn’t a humpback calf.”
Other researchers observe that Pitman’s theory makes sense, while noting that it’s perhaps impossible to really know what’s motivating the seemingly good-hearted humpbacks.
“Demonstrating it one way or the other is difficult unless you get into the brain of a humpback,” says Phillip Clapham, who oversees whale research for NOAA’s Marine Mammal Laboratory. “Animal behavior generally has a selective advantage, so one has to assume that this behavior, if it’s common, probably has some beneficial result.”
Humpback’s motivation aside, Pitman’s study also raises another question: Why would such a dramatic form of interspecies interaction only just now be getting noticed? The answer to that involves an interesting — and optimistic — fact about whale science. Most whale research has been conducted only since the 1970s; prior to that, 20th-century whalers had hunted most large whale populations nearly to the point of extinction. Now populations of many whale species are rebounding, especially humpbacks, which means that scientists have the opportunity to observe full-scale whale ecology for maybe the first time ever. Given that, it’s likely that many more discoveries await.
“People who study whales have been working in an environment that’s been largely empty of whales,” says Pitman. “Now that they’re coming back, we’re going to see some things we didn’t know about whales.”Kevin Hartnett is a writer in South Carolina. He can be reached at firstname.lastname@example.org.