When wild orangutans spot a predator, they let out a loud “kiss-squeak,” a call that sounds like a human smooching. That noise tells tigers and other enemies, “I’ve seen you,” scientists believe, and it also lets other orangutans know danger is near. Now, researchers report having heard orangutans making this call long after predators have passed—the first evidence that primates other than humans can “talk” about the past.
“The results are quite surprising,” says Carel van Schaik, a primatologist at the University of Zurich in Switzerland who was not involved in the work. The ability to talk about the past or the future “is one of the things that makes language so effective,” he says. That suggests, he adds, that the new findings could provide clues to the evolution of language itself.
Many mammals and birds have alarm calls, some of which include information on the type and size of a predator, its location and distance, and what level of danger it poses. But until now, researchers have never heard wild animals announcing danger after the fact.
Adriano Reis e Lameira, a postdoctoral student at the University of St. Andrews in the United Kingdom, was examining alarm calls in orangutans in Sumatra’s dense Ketambe forest, where the primates have been observed for nearly 40 years. He set up a simple experiment to investigate their alarm calls: A scientist draped in a tiger-striped, spotted, or plain sheet walked on all fours along the forest floor, right underneath lone female orangutans sitting in trees at heights of 5 to 20 meters above the ground.
Once they were spotted, the scientists would wait 2 minutes before moving out of sight. At that point, Lameira expected the orangutans to sound an alarm. But the very first female they tested, an older mother with a 9-year-old youngster, did not make a sound. “She stopped what she was doing, grabbed her infant, defecated [a sign of distress], and started slowly climbing higher in the tree,” Lameira recalled. “She was completely quiet.”
Lameira and his assistants waited—and waited. “It was frustrating. Twenty minutes passed. And then she finally did it.” But it wasn’t just one alarm. “She called for more than an hour.”
That was the longest Lameira had to wait for one of the seven females he tested. Still, all of them delayed making the alarm call—waiting an average of 7 minutes. He doesn’t think the apes were “petrified with fear” because they did not hesitate to corral their infants or to climb to a safer height. Instead, he thinks the females were quiet so as not to draw attention. “The mother saw the predator as most dangerous to her youngster and chose not to call until it was gone,” he says. Then, and only then, did she provide information, letting the infant learn about the danger that had passed, the team reports today in Science Advances.
Not responding immediately to a stimulus (in this case, a tiger) is considered a sign of intelligence, Lameira says. It’s a talent that goes along with other abilities found in great apes, such as long-term memory, intentional—rather than instinctive—communication, and fine control of the laryngeal muscles, all of which ultimately led to the evolution of language, he argues.
Simon Townsend, a comparative psychologist at the University of Zurich, agrees, saying the paper suggests the ability to discuss important events after they have happened is a “cognitive building block” of language. Van Schaik, however, thinks the orangutans’ ability is fundamental to the evolution of language itself, not simply another building block. Now, let me tell you again about the strange, scary, striped cat I saw …