The male Eurasian jay is an accommodating fellow. When his mate has been feasting steadily on mealworm larvae, he realizes that she'd now prefer to dine on wax moth larvae, which he feeds her himself. The finding adds to a small but growing number of studies that show that some animals have something like the human ability to understand what others are thinking.
"It's great for a first test of this ability in birds," says Thomas Bugnyar, a cognitive biologist at the University of Vienna in Austria who was not involved in the work. Scientists still debate about whether even our closest ape relatives can attribute an unseen, mental desire to another; some continue to argue that this is a peculiarly human talent. "But some of us think that some aspects of this ability should be found here and there in different species," Bugnyar says, "and so it is good to have this jay study to compare" with the other studies on primates, humans, and human children.
Male Eurasian jays feed their mates during courtship displays, says Ljerka Ostojić, a comparative psychologist and postdoc at the University of Cambridge in the United Kingdom who led the study. Because of that behavior, Ostojić and her colleagues thought that the jays might be good subjects for testing whether these birds understand their mates' desires. The group's previous research had shown that Eurasian jays and scrub jays can plan for the future. "It is commonly thought that any action animals take is determined solely by whatever they want at that moment," Ostojić says, "but the jays also plan for needs in the future."
In the new study, the scientists set out to see if the jays understood that other jays also had needs or desires—and that these were not necessarily the same as their own. Ostojić and colleagues put seven mated male-female pairs of jays through three experiments in an aviary at the university. The scientists measured how much food the birds needed to eat to reach a point of satiation.
The jays normally eat a diet of soaked dog biscuits, cheese, seeds, nuts, and fruit. But when given a choice, both males and females prefer mealworm larvae or wax moth larvae over their daily fare. The jays also have more of a hankering for wax moth larvae than mealworms. But, the scientists showed that when the birds have been prefed wax moth larvae, they readily switched to the larval mealworms. "This tells us that they were 'tired' of that food and wanted the other one," Ostojić says.
In the tests, the male and female pairs were then placed in adjacent compartments that were joined by a screened window. The females were given either wax moth larvae or mealworm larvae, while the males ate nothing but the maintenance diet. In one set of experiments, the male could see what his female ate through the window; but in another set, the window was covered, so that he could not watch her. Next, the experimenters gave each male 20 opportunities to choose between feeding his mate a wax moth larvae or a mealworm larvae. "If he is responding to her needs and what she might want next—and not to what he might want to eat—then he should choose the food she hasn't had," Ostojić explains.
And that's exactly what the males did—if they had watched their mates eating wax moth larvae, they passed them mealworm larvae instead, and vice versa. But when the males did not know what their females had dined on (because the window was covered), they fed them randomly from the two types of larvae, the team reports online today in the Proceedings of the National Academy of Sciences. "That really surprised me, because I thought the male would pick up on some behavior from the female, something that indicated what she wanted," Ostojić says. It was only when a male had observed his partner eating—and so had some idea that she was tired of eating wax moth larvae, for instance—that he selectively chose what to feed her next.
"It's a super cool finding, and suggests that the male birds are being more sensitive to the females than many human husbands," says Brian Hare, an evolutionary anthropologist at Duke University in Durham, North Carolina. "It's a new way of looking at the big picture of what other species know about mental states by using this cooperative, food-sharing behavior," Bugnyar adds. "It won't settle the debate, but it gives us a new method—and new species—to tackle this problem."