Can animals experience joy?
Well, sure, just look at my tuxedo cat, Tango. He has an evening ritual: He waits at the top of the bed for his brother Teddy, a large orange tabby cat that looks remarkably like a loaf of French bread, to pass by. Then Tango reaches out to snatch Teddy’s tail with apparent glee.
As animals ourselves, we think we see happiness in our fellow human beings all the time. The dogs frolic in the park; squirrels chase each other along tree trunks; Tango purrs his head at night trying to sleep on my face. Yet I know it may not be joy, for I cannot be certain of the emotions felt by a creature that cannot speak to me. Misinterpretation is possible. Sure, young squirrels might play, but adults are more likely to chase a rival for their stored acorns or fight over a potential mate.
For decades, scientists have struggled to identify or measure true joy—or “positive affect,” in scientific parlance—in nonhuman animals, even though they long assumed it existed. At the end of the 19th century, Charles Darwin wrote: “Lower animals, like man, manifestly feel pleasure and pain, happiness and misery. »
But in the 20th century, psychologists focused on strict behaviorism, which limited scientific study to actions that could be objectively counted. Think of Russian physiologist Ivan Pavlov and the dogs he conditioned to expect to eat when he rang a bell, giving him a measurable drooling response. Or the American psychologist BF Skinner, who put rats and pigeons in “Skinner boxes” where they were trained to press levers and peck keys to obtain rewards. This history has left scientists wary of anthropomorphism and subjective topics like feelings.
This is at least true for positive feelings – misery has received a lot of scientific attention. This is partly because researchers sought to understand and alleviate suffering, not only in animals, but also in people suffering from pain, depression, or other clinical problems. It’s also simple to measure a negative response, such as freezing in fear, against more subtle signs of contentment.
All this history has made the study of animal feelings largely taboo, a trend that has sometimes been resisted by researchers like the late Jaak Panksepp, an Estonian neuroscientist and an early leader in the study of emotions in the brain. In the early 2000s, when Panksepp reported that rats a sound similar to laughter when tickledscientists were doubtful; Ultrasonic calls are inaudible to human ears.
“Lower animals, like man, manifestly feel pleasure and pain, happiness and misery. »
Charles Darwin
“He had a hard time publishing it because people thought it was crazy,” says Michael Brecht, a neurobiologist at Humboldt University in Berlin. Skeptical but curious, Brecht conducted research that revealed that rats not only laugh, but also jump for joy And play hide and seek.
If scientists had better tools to measure positive emotions, they would be able to more deeply study the causes of happiness and how animals communicate it, with major implications for the mental health of animals in captivity.
This need inspired a bold group effort to attempt to develop a “joy-o-meter” – or more likely, a set of measures of happiness – that could be used to better understand many creatures, whether wild or captive, whether they walk, fly or swim.
“The overall goal of the project is to establish this serious scientific approach to positive emotions in animals, which has been extremely neglected,” says group member Erica Cartmill, a cognitive scientist at Indiana University in Bloomington. Cartmill studies great apes, but she knew that wouldn’t be enough to construct a universal metric. So she joined forces with researchers interested in studying the positive effects in dolphins and parrots.
Their work is part of a much-needed renewed interest in the study of animal emotions, says Marc Bekoff, an ethologist and professor emeritus at the University of Colorado at Boulder who studies canine play behavior. “For a long time, people have wondered whether dogs and other non-human mammals exhibit positive behaviors like happiness and joy, and sure enough, they do.” But, he adds, it is most likely different from human emotions.
As part of the joy-o-meter project, challenges quickly arose. Not only is it difficult to measure happiness, but it is also risky to predict what event might cause this state of joy. “Studying emotions is actually very difficult,” says Colin Allen, a project leader and philosopher at the University of California, Santa Barbara, who collaborates with Cartmill.
Simply put, Allen and his colleagues focused on a strict definition of joy as an intense, brief, positive emotion triggered by an event, such as encountering a favorite food or meeting with a friend. That kind of “woohoo!” » the moment seemed easier to assess than, say, continued mild contentment. Even with a strict definition, researchers face variations in joy triggers and responses across animals, including within the same species or group.
“You want to make sure that what you’re publishing is based in reality, instead of just guessing what’s going on in the animal’s mind,” says Heidi Lyn, a comparative psychologist at the University of South Alabama in Mobile who co-lead the project and was responsible for the dolphin studies as well as some of the monkey work.
These efforts by Lyn and her colleagues are important, says Gordon M. Burghardt, a biopsychologist and professor emeritus at the University of Tennessee at Knoxville. He is not involved in the Joy project, but has been studying animal play for over 40 years. In that work, Burghardt says, developing a definition with five criteria in 2004 helped identify play in various creatures, including mammals, birds, lizards, turtles, fish, octopuses and bumblebees.
“Positive affect is as worthy of scientific study as the study of pain and negative emotions,” Burghardt says. Not only could scientists discover how to improve the lives of captive animals, but they could also gain clues about human happiness. “What makes a good life?” » he asks. “These are the subjects that interest us the most. »
Do our close relatives feel joy?
The team began working on monkeys because its funder, the Templeton World Charity Foundation, believed the chances of success were best among humanity’s closest relatives. Bonobos are known for their playful behavior, including frequent sexual acts, which they use to create social bonds and resolve conflicts. Chimpanzees are considered more violent, although scientists have observed likely happy times among chimpanzee troops. Cartmill and Lyn’s groups have led the way, starting in 2022 with wild chimpanzees from the Fongoli Savanna Chimpanzee Project in Senegal; the bonobos of the Planckendael Zoo in Mechelen, Belgium; research bonobos at the Ape Initiative in Des Moines; and bonobos at the Jacksonville Zoo and Gardens in Florida.
Wild chimpanzees don’t have an easy life, says team primatologist Gal Badihi, who spent three months following a troop around Fongoli. They face hierarchies of dominance, competition and the constant search for food. Nonetheless, Badihi recorded some potentially joyous moments. For example, chimpanzees played with infants. A miner called Youssa turned out to be a real idiot, hanging upside down all the time. Other young chimpanzees liked to drink from each other’s mouths or roll around while laughing. When they reunited with their peers, the chimpanzees hugged and kissed each other. “The moments of joy stand out because they are quite rare,” says Badihi.
She is currently focusing her analysis on a panting sound, similar to low laughter, that chimpanzees often make during seemingly positive or social behaviors, as well as during situations where they want to communicate a positive intention or defuse a conflict. “It’s really similar to how we use laughter and smiles in social context as people,” says Badhi. (She now works at the German Primate Center in Göttingen.)
Badihi waited to observe possible moments of joy that occurred spontaneously, while another member of Cartmill’s team, behavioral biologist Daan Laméris, attempted to trigger possible moments of joy with the troop of bonobos at Planckendael ZOO. His attempts to introduce new toys into the bonobo enclosure illustrate how difficult it is to predict what makes the animals happy. Their favorites included a basketball, burlap bags and T-shirts – the latter more for ripping than wearing. But not all monkeys reacted the same way to joy triggers. Fewer bonobos appreciated piles of sawdust. Laméris hoped they would ride in it. And after carefully cleaning hundreds of used tennis balls, only one individual bothered to pick them up. The goal is to assess whether monkeys who play together tend to interact more later in the day, but Laméris isn’t ready to finalize his conclusions.
Another member of the Cartmill group, primatologist Sasha Winkler, successfully induced and measured signs of joy in the Ape Initiative’s bonobos. Winkler set out to reconstruct a feelings test based on observations that depression in people can lead to pessimistic judgments. Scientists who study rats adopted the idea, first to study whether rats living in less than optimal living conditions are pessimisticand later I discovered that rats that have recently enjoyed a good tickle are more optimistic. Similar tests of optimism have also been used with poultry to assess whether environmental improvements have made birds happier.
Winkler first set up the measurement system. She trained four adult bonobos to approach a black box expecting a tasty grape and ignore a white box that contained no such treat. The hypothesis was that if she then offered a gray box, an optimistic bonobo would be more likely to check it in anticipation of a gift.
Then she triggered the happy trigger: the sound of the baby bonobo’s laughter. Winkler prepared his subjects with a seven-and-a-half-minute audio recording of laughter or a neutral wind-like sound before taking out the boxes. After hearing the laughter, the bonobos more likely to approach gray boxesreported Winkler in 2025 in Scientific reports. “This is evidence that they feel better after hearing laughter,” says Winkler, now a postdoctoral researcher at Duke University in Durham, North Carolina.
Try your luck with a surprise
The researchers trained the bonobos to expect that a black box would always contain a grape, whereas a white box never would. The monkeys chose to approach the black boxes and ignore the white ones. If they didn’t like a box, they could press a button (denoted “a”, on the left) to indicate the next offer.
The scientists then played sounds before a testing session: either the sound of a baby bonobo laughing or the sound of the wind. Then they came up with a new gray box.
Bonobos who heard recorded laughter were more likely to take a chance and approach the gray box, which contained a grape 50% of the time. They preferred the darker gray boxes, perhaps because they looked more like the black boxes containing the grapes.
Another test that researchers are conducting across multiple species is a “godsend” experiment, offering a happy surprise as a trigger for joy. Lyn performed this test with bonobos from the Ape Initiative and the Florida Zoo, using an unexpected abundance of treats as a trigger.
The experimenter first showed a grape to a bonobo, then hid it between two overturned trash cans. The researcher then revealed the grape for the monkey to eat. Until now, the treat was entirely expected. But after repeating this five times, the researcher performed a magic trick. Unnoticed by the bonobos, there was a third container under the other two. And sandwiched between that bottom and middle square were 10 grapes – the jackpot!
This revelation was a godsend. In response, the Jacksonville bonobos made hoots that ape researchers call “eating sounds.” That in itself wasn’t much of a surprise, but other studies indicate people might be aware. but general happiness. The Des Moines bonobos nodded instead, so that’s another candidate signal of joy, Lyn says.
The team also set up a social bonanza. They organized video calls between the bonobos and their keepers on an iPad. The happy surprise was the appearance of a guardian that the bonobo had not seen for a while. Again, the monkeys were either looking or nodding, suggesting that these behaviors could be about more than just eating. “Maybe they’re just ‘happy people’,” Lyn speculates.
Parrots making snowballs
Once research on monkeys began to show promising results, the Templeton Foundation began funding studies on parrots and dolphins in 2024.
The parrots studied are keas, large, intelligent birds found in the mountains and forests of New Zealand’s South Island. Team investigator Ximena Nelson, a behavioral biologist at the University of Canterbury in Christchurch, New Zealand, already had plenty of reason to suspect that the birds were experiencing joy. In particular, she noticed that they seemed to like sunny, snowy weather. Nelson saw them making snowballs and sledding on the roofs of ski lodges. “It’s anthropomorphic, there’s no doubt about it,” she says. “But I spent a lot of time in the mountains with these kea, and that’s one thing, I’m sure.”
