Animals experience joy. Scientists want to measure it

Can animals experience joy?

Well, of course — just look at my tuxedo cat, Tango. He has an evening ritual: He waits atop the bed for his brother Teddy, a fat orange tabby with a remarkable resemblance to a loaf of French bread, to stroll by. Then Tango reaches out to snatch at Teddy’s tail with apparent glee.

As animals ourselves, we think we see happiness in our fellow creatures all the time. Dogs romp in the park; squirrels chase each other up and down tree trunks; Tango purrs his head off at night while attempting to sleep on my face. Yet I know that it may not be glee because I can’t be certain what emotions are felt by a creature that can’t speak to me. Misinterpretation is possible. Sure, young squirrels could be playing, but adults are more likely to be chasing off a rival for their stored acorns or competing for a potential mate.

For decades, scientists have struggled to identify or measure true joy — or “positive affect,” in sci-speak — in nonhuman animals, even though they’ve long assumed it exists. In the late 19th century, Charles Darwin wrote, “The 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 tallied. Think Russian physiologist Ivan Pavlov and the dogs he conditioned to expect food when he rang a bell, giving him a measurable drooling response. Or American psychologist B.F. Skinner, who put rats and pigeons in “Skinner boxes” where they were trained to push levers and peck keys for rewards. That history left scientists wary of anthropomorphism and subjective topics like feelings.

That’s true for positive feelings, at least — there has been loads of scientific attention on misery. In part, that’s because researchers aimed to understand and relieve suffering, not just in animals but in people experiencing pain, depression or other clinical problems. It’s also straightforward to measure a negative response, such as freezing in fear, compared to subtler signs of contentment.

All this history made the study of animal feelings largely taboo, a trend bucked on occasion by researchers like the late Jaak Panksepp, an Estonian neuroscientist and early leader in the study of emotions in the brain. In the early 2000s, when Panksepp reported that rats make a laughter-like sound when tickled, scientists were doubtful; the ultrasonic calls are inaudible to human ears.

“The lower animals, like man, manifestly feel pleasure and pain, happiness, and misery.”

Charles Darwin

“He had problems publishing it at all because people thought it was crazy,” says Michael Brecht, a neurobiologist at Humboldt University of Berlin. Skeptical but curious, Brecht did research that found rats not just laughing, but also jumping for joy and playing hide-and-seek.

If scientists had better tools to measure positive emotions they’d be equipped to more deeply investigate the causes of happiness and how animals communicate it, with major implications for mental health among captive animals.

This need has inspired an audacious group effort to try to develop a “joy-o-meter” — or more likely, a set of happiness metrics — that could be used to better understand many critters, whether they are wild or captive, whether they walk, fly or swim.

“The overall goal of the project is to establish this serious, scientific approach to positive emotion in animals, which has been hugely overlooked,” says Erica Cartmill, a member of the group and a cognitive scientist at Indiana University Bloomington. Cartmill studies great apes, but she knew that they wouldn’t be enough to build a universal metric. So she joined up with investigators with interest in studying positive affect in dolphins and parrots.

Their work is part of a much-needed surge of interest in studying animal emotions, says Marc Bekoff, an ethologist and emeritus professor at the University of Colorado Boulder who studies canine play behavior. “For a long time, people wondered whether dogs and other nonhuman mammals experienced positive behaviors like happiness and joy, and of course they do.” But, he adds, it is most likely different from human emotions.

In the joy-o-meter project, challenges quickly arose. It’s not only tricky to measure happiness, it’s also dicey to predict what event might induce that joyful state. “Studying emotions is actually really hard,” says Colin Allen, a project lead and philosopher at the University of California, Santa Barbara who collaborates with Cartmill.

To keep it simple, Allen and his colleagues have focused on a strict definition of joy as an intense, brief, positive emotion triggered by some event, such as encountering a favorite food or a reunion with a friend. That kind of “woohoo!” moment seemed easier to assess than, say, ongoing mild contentment. Even with a strict definition, the researchers are contending with variations in joy triggers and responses from one animal to the next, including within the same species or group.

“You want to make sure that what you’re putting out there is based on reality, as opposed to just guessing what is happening in the animal’s mind,” says Heidi Lyn, a comparative psychologist at the University of South Alabama in Mobile who is a co-leader of the project and is in charge of the dolphin studies as well as some of the ape work.

These efforts by Lyn and colleagues are important, says Gordon M. Burghardt, a biopsychologist and emeritus professor at the University of Tennessee, Knoxville. He is not involved in the joy project, but has studied animal play for more than 40 years. In that work, Burghardt says, coming up with a definition with five criteria in 2004 made it possible to identify play in diverse creatures including mammals, birds, lizards, turtles, fish, octopuses and bumblebees.

“Positive affect is as much worthy of scientific study as studying pain and negative emotions,” Burghardt says. Not only might scientists figure out how to better the lives of captive animals, they might get some clues to human happiness, too. “What is it that makes a good life?” he asks. “Those are the topics that are most worthwhile for us.”

Do our nearest relatives feel joy?

The team began the work in apes because its funder, the Templeton World Charity Foundation, thought the odds of success were best in humankind’s closest relatives. Bonobos are known for playful behavior, including frequent sex acts they use to create social bonds and resolve conflicts. Chimpanzees are considered more violent, though scientists have observed what are likely happy times in chimp troops. Cartmill’s and Lyn’s groups led the way, starting in 2022 with wild chimps at the Fongoli Savanna Chimpanzee Project in Senegal; zoo bonobos at ZOO Planckendael in Mechelen, Belgium; research bonobos at the Ape Initiative in Des Moines; and bonobos at the Jacksonville Zoo and Gardens in Florida.

Wild chimps don’t have easy lives, says team primatologist Gal Badihi, who spent three months following a troop around Fongoli. They contend with dominance hierarchies, competitions and the ongoing search for food. Nonetheless, Badihi recorded potentially joyful moments. For example, chimps played with infants. A juvenile called Youssa proved to be quite the goofball, hanging upside down all the time. Other young chimps liked to drink from each other’s mouths or roll around giggling. When reuniting with their fellows, chimps would embrace and kiss. “The joyous moments kind of stick out because they are quite rare,” says Badihi.

She’s currently focusing her analysis on a panting sound like unvoiced laughter that chimps often made during those apparently positive or social behaviors, as well as during situations where they wanted to communicate positive intent or de-escalate conflict. “It’s really similar to how we use laughter and smiles across social context as people,” Badhi says. (She now works at the German Primate Center in Göttingen.)

Badihi waited to observe potential moments of joy that occurred spontaneously, while another Cartmill team member, behavioral biologist Daan Laméris, tried to trigger possible joyful moments with the bonobo troop at ZOO Planckendael. His attempts to introduce novel toys to the bonobo enclosure illustrate how hard it is to predict what makes animals happy. Their favorites included a basketball, burlap sacks and T-shirts — the latter more for tearing than for wearing. But not all apes responded the same way to the joy triggers. Fewer bonobos liked the piles of sawdust Laméris hoped they would roll around in. And after he’d painstakingly cleaned hundreds of used tennis balls, only one individual bothered to collect them. The goal is to assess whether apes that 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, has succeeded both in inducing and measuring signs of joy with the bonobos at the Ape Initiative. Winkler set out to re-enact a test of feelings based on observations that depression in people can lead to pessimistic judgments. Scientists studying rats adopted the idea, first to study if rats in less-than-optimal living conditions are pessimistic, and later to find that rats that recently enjoyed a good tickle are more optimistic. Similar optimism tests have also been used with poultry to assess whether environmental improvements made the birds happier.

First, Winkler set up the measurement system. She trained four adult bonobos to approach a black box in expectation of a tasty grape, and to ignore a white box that held no such treat. The presumption was that if she then offered a gray box, an optimistic bonobo would be more likely to check it out in anticipation of a goody.

Then she brought in the happiness trigger: the sound of baby bonobo laughter. Winkler primed her subjects with an audio recording of either seven and a half minutes of laughter or a neutral windlike sound before bringing out the boxes. After hearing the laughter, the bonobos were more likely to approach the gray boxes, Winkler reported in 2025 in Scientific Reports. “That was evidence that they feel better after hearing laughter,” says Winkler, who is now a postdoctoral fellow at Duke University in Durham, N.C.

Another test the researchers are conducting in multiple species is a “windfall” experiment, offering a happy surprise as the joy trigger. Lyn tackled this test with bonobos at the Ape Initiative and the Florida zoo, using an unexpected bounty of treats as the trigger.

First, the experimenter showed a bonobo a grape, then hid it between two overturned bins. The researcher then revealed the grape for the ape to eat. So far, 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 underneath the other two. And sandwiched between that bottom box and the middle one were 10 grapes — jackpot!

That reveal was the windfall. In response, the Jacksonville bonobos made hooting sounds that are known to ape researchers as “food peeps.” That alone wasn’t much of a surprise, but further studies indicate the peeps may be about general happiness. The Des Moines bonobos nodded their heads instead, so that’s another candidate joy signal, Lyn says.

The team also set up a social windfall. They arranged video calls between bonobos and their keepers on an iPad. The happy surprise was the appearance of a keeper the bonobo hadn’t seen in a while. Again, the apes peeped or nodded, suggesting those behaviors might be about more than food. “Maybe they’re just ‘happy peeps,’” Lyn speculates.

Parrots that make snowballs

Once the ape research began to yield promising results, the Templeton Foundation began funding the parrot and dolphin studies in 2024.

The parrots under study are keas, big, smart 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 the birds experience joy. In particular, she noticed they seem to love sunny, snowy weather. Nelson has seen them make snowballs and sled down the roofs of ski huts. “That is anthropomorphizing, there’s no doubt about it,” she says. “But I’ve spent a lot of time up in the mountains with these kea, and it’s a thing, I’m sure of it.”

Nelson’s previous research on the curious, mischievous parrots revealed that they make playful “warble calls” that are contagious, like human giggle fits. Playing a warble recording to a wild kea, juvenile or adult, sets off a playful response. “It will start, like, tap-dancing,” Nelson says. “They start playing, and they start warble calling.”

Based on this finding, Nelson and zoologist Alex Grabham, a postdoc in her group, reasoned they could use the warble calls as an easy joy trigger for their experiments with a kea flock, sometimes called a “circus,” at the Willowbank Wildlife Reserve in Christchurch. But they immediately hit a snag. Born and raised in captivity, these parrots had never heard a warble call — and they hated it. When the researchers played the tape, the birds flew around making distress calls. “They just went mental,” Nelson says.

After some time back at the drawing board, Grabham returned to the circus with new potential joy triggers.

One was a favorite food for the kea windfall experiment, a variation on what Lyn had done with the bonobos. First the keas got a carrot, which they consider “sort of a ‘meh’ food,” Nelson says. Then another carrot, and another carrot. Then, the windfall: peanut butter!

For his part, Grabham hopes to use changes in keas’ body temperature as a measure of joy. Body temperature changes with stress, so perhaps it does with happiness, too. He aimed an infrared camera at the area around the birds’ eyes where there are no feathers to get in the way. The team is still analyzing the data, which came out noisy; the temperature seems to make more of a wobble, rather than go straight up or down.

Making measurements of biological markers, and not just behaviors, is important, says Sergio Pellis, an ethologist and animal play expert at the University of Lethbridge in Canada. “Just looking at the behavior from the outside may not be sufficient to make a judgment about how much the animals are enjoying this,” says Pellis, who is not involved in the joy-o-meter project. “There may be situations when they’re faking it.”

For example, Pellis says, sometimes horses and dogs look like they’re playing, but their levels of the stress hormone cortisol indicate they’re not having a good time.

Grabham is also analyzing samples from a different experiment inspired by keas’ love of snow. This time, the captive circus cooperated. Grabham dumped machine-made snow on the aviary’s hillside in the hopes of triggering joy. He’s pretty sure he succeeded. “The kea were all over it,” he says. “My instinct is that they were having a good time.” Some played alone; some held snow fights; one pushed a snowball toward a researcher.

To measure this possible joy more objectively, the researchers collected poop from playing parrots to measure levels of the bird versions of the hormones cortisol and oxytocin. To gather fecal samples, each of the 12 parrots was assigned a human researcher to follow the bird around with a spatula and test tubes. Grabham estimates each bird produced about five specimens in the one-day experiment, but one, called Plankton, offered up sizable samples every 20 minutes. Grabham is analyzing the hormone data now.

Again, Nelson expects the data to be noisy because hormone levels can be influenced by factors like the time of day, the animal’s sex and whether it is molting. This variance in how joy may be expressed by individual animals has been an ongoing challenge.

And as with Laméris’ apes, individual parrots had varying interest in joy triggers, too — and in whether they expressed interest in participating in the experiments at all. One adolescent kea, called Megatron and described by Grabham as “a little menace,” eagerly bounded along behind the scientist as he headed for Megatron’s testing platform. But another, Mystique, tended to ignore the scientist’s calls; she’d rather push a leaf back and forth in the water.

That doesn’t mean it’s impossible to trigger and measure joyful behaviors, Grabham says. But “one experiment might not fit all.”

While he continues analyzing data from the circus at the wildlife reserve, data from wild keas has shored up Nelson’s beliefs about their happiness in sunny, snowy weather. She sent a student with a video camera to tramp up and down New Zealand’s mountains and film the birds. In the resulting videos, the keas were four times more likely to warble if the sun shone.

“It is intriguing that keas make a warble song during play, and that it is four times more frequent when the sun is shining emphasizes the potential joyful aspect of the display,” says Nicky Clayton, an expert in bird behavior and cognition at the University of Cambridge who was not involved in the study.

“Given the difficulties,” says Nelson, “I think we’ve actually made quite a lot of progress.”

Behind the dolphin’s smile

Like keas in the sun, dolphins sure look like they’re having fun, leaping through the bow waves of boats, blowing bubble rings or playing catch with bits of seaweed. But their characteristic “smile” is frozen in place and says nothing about their emotional state.

They have a few things in common with great apes: intelligence, yes, but other qualities too. Like bonobos, they’re known for voracious sexual appetites. Like chimps, they can sometimes be violent, kidnapping females, occasionally killing baby dolphins and smacking around harbor porpoises. And sometimes their play objects are unfortunate sea turtles or seals.

Lyn’s 2020 study with dolphins illustrates how valuable a joy-o-meter would be to monitor the well-being of captive animals. The Association of Zoos and Aquariums requires accredited facil­ities to provide enrichment, but not every toy provokes positive behaviors.

In that study, the researchers provided novel items like bubble generators or barrels coated in artificial turf. The biggest response was to a 3-foot-long block of ice, and it wasn’t a positive one — at least not at first. The two dolphins, Bo and Buster, initially fled, then returned to investigate. Overall, dolphins tended to avoid the novel objects — hardly a rousing endorsement for their potential to induce joy.

And as with apes and parrots, vocal calls may be the key to understanding dolphin joy. Other dolphin researchers have defined the “victory squeal” as a sound the animals make when they catch a fish or receive a fish prize from their trainers.

They suggest it reflects release of the reward chemical dopamine in the brain. Once trained, dolphins make the same sound after they complete a task but before they get the fish reward, or even in the open ocean where their trainers aren’t nearby. It’s as if it’s a sort of “I did it!”

Lyn’s team has observed similar squeals in other contexts, such as when dolphins receive a surprise treat, like a toy or bucket of ice. She hopes to perform windfall experiments to measure if the dolphins squeal more in the moments after they get an unexpected treat, like a favorite toy.

“While it is hard to know how animals experience emotions or how similar those impressions are to our own subjective emotional experiences, the cetacean victory squeal does seem 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 part of the study.

Preliminary data indicate that squeals may have a social function, too. If their trainers are also screaming with joy, the dolphins seem to make bigger or more frequent squeals. And they do it when socializing with other dolphins, such as swimming together. “It seems to very much be this sort of communicative pattern,” Lyn says.

While there’s still plenty more work to do, the project researchers are excited about the progress they’ve made and what’s to come. After scientists spent so many decades focusing on unhappy feelings in an effort to reduce negative experiences for animals in captivity, kea researcher Nelson says, “it’s just nice to turn the tables and think about the positive.” Her own reasons for studying animal happiness are even simpler than that: “Because it gives me joy.”