Eurasian Jays Recognize Long-Term Mates

Lead researcher Ljerka Ostojic with an Eurasian Jay (Photo Credit: Julia Leijola/ CC-BY-NC-SA)

Valentine’s Day is right around the corner, and perhaps guys looking to impress their gal should clue in to the behavior of male jays: Eurasian jays can interpret changes in what their mates desire—when it comes to food, anyway.

The birds, which inhabit woodlands and forests from Western Europe to India, feed each other everything from beetles and worms to acorns and berries during courtship displays. This food-sharing behavior got researchers at Cambridge University’s Department of Psychology in England wondering if jays could interpret the internal dietary desires of their mate.

To find out, they conducted three experiments using seven pairs of mated jays housed in outdoor aviaries. They fed all of the males a diet of soaked dog biscuits, cheese, seeds, nuts, and fruit. During the experiments the females were fed either this “maintenance” diet, wax moth larvae, or mealworm larvae.

In one experiment, they placed the male and female in a compartment separated by a screened window. Lead researcher Ljerka Ostojic and her colleagues fed the females either wax moth larvae or mealworm larvae—only one type—while the male jay observed. When the screen was removed, males were given access to two bowls—one containing wax moth larvae, the other mealworm larvae—from which to share food with their mate. Males shared more of the type of larvae their mate hadn’t had access to, indicating that when a fella saw what his gal had previously eaten, he knew she’d want something different now. (Kind of like filling up on a sandwich, turning down another when it’s offered to you, but having room for some ice cream.)

Turns out that being able to see what the female is eating is crucial. When scientists placed a cover between the two compartments, preventing the male from seeing what his partner consumed, he fed her a mixture of both larvae.

And when the male only had to feed himself, he fed himself exactly what he wanted, indicating that eurasian jays can tend to their mates when necessary and recognize that they have different desires other than their own.

Researchers state that because males needed to witness their partner consume one food option, known as “specific satiety,” in order to feed them the other, males can tune into the females’ internal state.

“Ascribing internal states to other individual requires the basic understanding that others are distinct from the self and others’ internal states are independent from, and differ from, one’s own,” the authors write in the study, published in PNAS.

For Eurasian jays food sharing is an important courtship behavior that plays a crucial role in forming and maintaining pair bonds, the authors say, so the ability of a male to interpret his partner’s internal state may make him more valuable as a mate.

These findings fuel the pre-existing debate on whether humans are the only species able to interpret another’s mental desires. Thomas Bugnyar, a cognitive biologist at the University of Austria that is unaffiliated with the study told ScienceNOW, “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. It won't settle the debate, but it gives us a new method—and new species—to tackle this problem."

As for guys needing some advice around Valentine’s Day, Ostojic has a few thoughts. “A comparison might be a man giving his wife chocolates. The giving and receiving of chocolates is an important ‘pair-bonding’ ritual,” she says.  “But, a man that makes sure he gives his wife the chocolates she currently really wants will improve his bond with her much more effectively- getting in the good books, and proving himself a better life partner.”