Life as a carnivore is often tough. You have to catch your meals on the run, and depending on the predator, more than 80 percent of attempts to grab a bite can end in failure.
Because of this, scientists have often assumed that predators take what they can get from their prey and can’t afford to be picky. But gruesome scenes in South Africa have turned that idea on its head: killer whales are taking down a dozen or more sharks in one day—and rather than feasting on every meaty morsel, the orcas are meticulously cutting out the livers and leaving the rest of their kill to rot. This preference for a particular organ is not odd for orcas, according to marine biologists. They’re known around the world for going after the choicest cuts from their prey.
“One of the best well-known examples is from Eden, New South Wales, Australia, where whalers and killer whales cooperatively hunted baleen whales,” says Isabella Reeves, a doctoral candidate in marine biology at Flinders University in Australia. These 19th-century whalers collected the bulk of the carcass, but the orcas would eat the baleen whales’ tongue through the lower jaw, a tacit agreement known as the “law of the tongue,” Reeves says. To this day, orcas in various regions still chow down on whale tongue, she says.
Near the South African town of Gansbaai in late February 2023, 20 dead sharks washed onshore with their belly ripped open and their liver missing. The carnage was the work of just two orcas, nicknamed Port and Starboard, who are known to hunt sharks in the region. A third orca in the area has also been observed targeting shark livers, suggesting that Port and Starboard might be teaching their methods to their neighbors, says Alison Towner, a doctoral candidate at Rhodes University in South Africa. Orcas have also demonstrated a taste for shark liver around the globe, says Lauren Meyer, a food web ecologist at Flinders University. Dating back to at least the 1950s, dead sharks whose liver was extracted by orcas have been observed in Argentina and New Zealand and off the coast of California, Meyer says.
Near Gansbaai, orcas have been observed ripping livers out of great white sharks and sevengill sharks since at least 2015, says Ralph Watson, a marine biologist at South Africa’s Dyer Island Conservation Trust. Livers make up about a third of sharks’ body weight and are rich in a nutritious oil called squalene, making them highly appealing to orcas, Watson says. “Rough calculations suggest a single white shark liver might sustain a single orca for a day,” he adds.
In comparison, the cartilage and muscle that make up most of the rest of a shark carcass might not be worth the effort, Watson says.
Orcas also seem to enjoy penguin breast meat and sunfish intestines, Meyer says. She, Towner and Reeves are currently conducting research to try to understand what nutrients orcas might be gleaning from these portions of their prey. One advantage, Meyer says, is that these body parts are nice and soft. “As a long-lived animal with a single set of teeth, minimizing tooth wear may be the key to a long and healthy life, supporting the selection of soft tissues where feasible,” she says.
And it turns out orcas, which are members of the dolpin family, aren’t the only predators out there with a taste for specific organs. Evidence is mounting that other carnivores, both on land and in the sea, may go after certain prey to maximize their energy intake or nutrition, or both.
“Sometimes there’s plenty of food available, or it might be that prey is rare, but there are other pressing priorities that might cause them to feed a certain way first,” says Kevin Kohl, an animal physiologist and microbial ecologist at the University of Pittsburgh. “We’ve overlooked a lot of nuance about carnivore biology.”
Great white sharks scavenging on the bonanza of a whale carcass select blubber-rich spots first and sometimes even spit up fleshy chunks in favor of going back for fattier bites, according to a 2013 study in the journal PLOS ONE. Cape fur seals enjoy dining on the energy-rich livers of blue sharks. Although harbor seals in Alaska will eat everything but the head when they catch a male salmon, they focus on just the egg-rich bellies of female salmon, according to a 2010 study.
Eggs are often a tempting meal for predators, says Christopher Dickman, a terrestrial ecologist at the University of Sydney. Female thorny devils, a spiky lizard endemic to Australia, are a favorite target for falcons during breeding season because the lizards hold dozens of eggs in their belly. In falcon nests, “you’ll find two to three dozen carcasses of the thorny devils, all with the bellies ripped open and the eggs gone,” Dickman says. “Eggs are a great nutritious source of pretty much everything you could want.”
Terrestrial predators also sometimes show preferences for certain body parts. Wolves, for example, go after the guts of deer and other large prey. Brown and black bears focus on the oily brains and nutritious roe of salmon when the fish are abundant and deign to chow down on whole fish only in years when salmon aren’t plentiful.
Dickman has found that lesser hairy-footed dunnarts (Sminthopsis youngsoni) and Wongai ningaui (Ningaui ridei)—small mouselike marsupials in Australian deserts—preferentially eat the abdomens and thoraxes of their insect, spider and centipede prey. “They don’t like the legs very much,” Dickman explains.
He and his colleagues have also found that these marsupials deliberately hunt down wolf spiders, despite research showing that wolf spiders aren’t any more nutritious than other arthropod prey. In this case, Dickman says, wolf spiders eat other insects that dunnarts also like to eat, so hunting wolf spiders not only provides a tasty meal but also removes a source of competition for other food.
It’s still unclear, though, how much wild animals are aware of their nutritional needs and to what extent they might make deliberate choices based on any requirements for certain vitamins or minerals, not just energy, Kohl says. Humans might crave a green salad after several meals of starchy food. Herbivores, too, are known to forage for certain nutrients among the plants they eat, he says. Do carnivores experience similar cravings? It’s hard to say.
“I think we have a poor understanding of what animals are experiencing in their day-to-day lives,” Kohl says.
