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.”
playful and contagious “chirps”as if human laughter matched. Playing a recorded chirp to a wild kea, juvenile or adult, triggers a playful response. “It’s going to start, like tap dancing,” Nelson says. “They start playing and they start chirping.”Based on this finding, Nelson and zoologist Alex Grabham, a postdoctoral fellow in his group, thought they could use chirps as an easy joy trigger for their experiments with a flock of kea, sometimes called a “circus”, in Christchurch’s Willowbank Wildlife Reserve. But they immediately ran into a problem. Born and raised in captivity, these parrots had never heard a chirp – and they hated it. When the researchers played the tape, the birds flew everywhere making distress calls. “They went crazy,” Nelson says.
After some time back at the drawing board, Grabham returned to the circus with new potential joy triggers.
One of them was the favorite food of the kea experiment, a variation of what Lyn had done with the bonobos. The keas were first given a carrot, which they consider “kind of ‘meh’ food,” Nelson says. Then another carrot, and another carrot. Then, the manna: peanut butter!
For his part, Grabham hopes to use Keas’s body temperature changes as a measure of joy. Body temperature changes with stress, and perhaps also with happiness. He pointed an infrared camera at the area around the birds’ eyes, where no feathers bother them. The team is still analyzing the data, which turned out to be noisy; the temperature seems to waver more, rather than going straight up or down.
It’s important to measure biological markers, not just behaviors, says Sergio Pellis, an ethologist and animal play expert at the University of Lethbridge in Canada. “Just observing the behavior from the outside may not be enough to judge how much the animals like it,” says Pellis, who is not involved in the Joy-O-Meter project. “There may be situations where they are pretending.”
For example, Pellis says, sometimes horses and dogs look like they’re playing, but their levels of cortisol, the stress hormone, indicate they’re not having a good time.
Grabham also analyzes samples from another experiment inspired by Keas’s love of snow. This time, the captive circus cooperated. Grabham dumped artificial snow on the side of the aviary in hopes of sparking joy. He’s almost sure he succeeded. “The kea were everywhere,” he says. “My instinct is that they were having a good time.” Some played alone; some organized snow fights; one of them pushed a snowball toward a researcher.
To more objectively measure this possible joy, researchers collected the droppings of playful parrots to measure levels of the bird versions of the hormones cortisol and oxytocin. To collect fecal samples, each of the 12 parrots was assigned a human researcher to follow the bird with a spatula and test tubes. Grabham estimates that each bird produced about five specimens during the day-long experiment, but one, called Plankton, provided significant samples every 20 minutes. Grabham is currently analyzing hormonal data.
Again, Nelson expects the data to be noisy, as hormone levels can be influenced by factors such as time of day, the sex of the animal and whether it is shedding. This variation in how joy can be expressed by individual animals poses an ongoing challenge.
And as with the Laméris monkeys, individual parrots also had varying interest in joy triggers – and whether or not they expressed interest in participating in the experiences. A teenage kea, called Megatron and described by Grabham as “a little menace”, eagerly bounded behind the scientist as he headed towards Megatron’s testing platform. But another, Mystique, tended to ignore the scientist’s calls; she prefers to push a leaf back and forth in the water.
That’s not to say it’s impossible to trigger and measure joyful behaviors, says Grabham. But “one experience might not be right for everyone.”
As he continues to analyze data from the wildlife preserve’s cirque, data from wild keas has reinforced Nelson’s beliefs about their happiness in sunny, snowy weather. She sent a student with a video camera to travel through the mountains of New Zealand and film the birds. In the resulting videos, keas were four times more likely to chirp if the sun was shining.
“It is fascinating that keas emit a chirping song during play, and that this is four times more frequent when the sun is shining, underscoring the potentially joyful aspect of the spectacle,” says Nicky Clayton, an expert in bird behavior and cognition at the University of Cambridge who was not involved in the study.
“Given the challenges,” Nelson says, “I think we’ve made a lot of progress.”
Behind the smile of the dolphin
Like keas in the sun, dolphins really look like they are having funjumping through the bow waves of boats, blowing rings of bubbles or playing catch with pieces of seaweed. But their characteristic “smile” is fixed and says nothing about their emotional state.
They have a few things in common with the great apes: intelligence, certainly, but other qualities too. Like bonobos, they are known for their voracious sexual appetite. Like chimpanzees, they can sometimes be violent, kidnapping females, occasionally killing baby dolphins, and striking harbor porpoises. And sometimes their play objects are unfortunate sea turtles or seals.
Lyn’s 2020 study on dolphins illustrates how valuable a joy-o-meter would be for monitoring the welfare of captive animals. The Association of Zoos and Aquariums requires accredited facilities to provide enrichment, but not all toys elicit positive behaviors.
In this study, researchers provided new elements such as bubble generators or barrels covered with artificial grass. The biggest answer was a 3-foot-long block of ice, and it wasn’t positive — at least not at first. The two dolphins, Bo and Buster, first ran away, then returned to investigate. Overall, the dolphins tended to avoid the novel objects – hardly an enthusiastic endorsement of their potential to cause joy.
And as with monkeys and parrots, vocal calls may be the key to understanding dolphin joy. Other dolphin researchers have defined the “victory cry” like the sound animals make when they catch a fish or receive a fish prize from their trainers.
They suggest this reflects the release of dopamine, a reward chemical, in the brain. Once trained, dolphins make the same sound after completing a task, but before they receive the fish rewardor even in the open sea where their trainers are not nearby. It’s like it’s some sort of “I did it!” »
Lyn’s team has observed similar calls in other contexts, such as when dolphins are given a surprise treat, such as a toy or a bucket of ice. She hopes to carry out unique experiments to measure whether dolphins cry more in the moments following an unexpected treat, such as their favorite toy.
“Although it is difficult to know how animals feel their emotions or how similar these impressions are to our own subjective emotional experiences, the cetacean victory cry appears to be associated with objectively positive events in a cetacean’s life,” says Jason Bruck, a behavioral biologist at Stephen F. Austin State University in Nacogdoches, Texas, who was not involved in the study.
Preliminary data indicates that screams may also have a social function. If their trainers also shout with joy, the dolphins seem to emit louder or more frequent cries. And they do this when socializing with other dolphins, such as swimming together. “It seems to be that kind of communication pattern,” Lyn says.
Although there is still much work to be done, project researchers are excited about the progress they have made and what lies ahead. After scientists spent so many decades focusing on feelings of unhappiness in an effort to reduce the negative experiences of animals in captivity, Kea researcher Nelson says, “It’s just nice to turn the situation around and think about the positive.” » His own reasons for studying animal happiness are even simpler than that: “Because it brings me joy.” »
