Animal personalities can play a big role in saving species

Much like his ninja namesake, Naruto the white-lipped peccary was a bit of a loner.

Named after the titular character from a popular manga and anime, Naruto was the youngest male and one of the least social in his group of 17 peccaries, all of whom were born and raised in captivity at the Laboratory of Applied Ethology at the State University of Santa Cruz in Ilhéus, Brazil.

Destined for reintroduction into Brazil’s Estação Veracel Private Natural Heritage Reserve and the Pau-Brasil Ecological Station, the peccaries were each given a personality test of sorts by lab researchers. The piglike mammals were video recorded as they went about their daily lives, resulting in 17 hours’ worth of behavioral data. Their aggressive actions, friendly touches and moments of exploration were tallied so that the peccaries could be ranked in traits such as boldness and sociability.

The goal was to determine whether an individual peccary’s behavioral traits influenced its survival when released into the wild. White-lipped peccaries (Tayassu pecari) are listed as vulnerable by the International Union for Conservation of Nature, or IUCN. In Brazil, the size of the species’ historical range had plunged by 60 percent by 2020, and past efforts to reintroduce them had met limited success.

Around the globe, scientists are increasingly recognizing how a reintroduced animal’s personality can impact how both individuals and groups fare in the wild. Such work is part of a growing trend to infuse the study of personality, and how it affects behavior, into conservation. When working with wild animals and tight budgets, personality tests may not always be possible. But understanding animal personality could help conservationists choose which individuals stand the best chance of surviving — helping to restore populations threatened with extinction.

For Naruto, his loner personality may have ultimately been his undoing.

Naruto’s behavior stood out to Selene Nogueira, an ethologist at the university and leader of the lab’s peccary project. “He was the last one to eat and then was thinner than the others,” Nogueira says. “I think his personality was a little bit shy.” Once the peccaries were released, Naruto continued his asocial ways. His wanderings helped the group disperse. But less than a year after the release, researchers found him limping with deep bite marks, probably from a jaguar or puma. He died three days later.

Peccaries are known to fend off predator attacks when in a group. Sure enough, the rest of the peccaries fared better, and now, after about two years, the group has welcomed 10 babies. From her study, Nogueira generally concluded that, for a released group of peccaries to be successful, they need a mixture of personality types — asocial adventurers to go off and nudge the group along, as Naruto did, and social butterflies that stick together.

For scientists working in the forests of Brazil in the 20th century, the mere idea of peccary personalities would have been laughable. But Nogueira’s work is part of a wave of research in the last two decades showing that personalities aren’t just the purview of peccaries — they’re everywhere in the animal world.

A plethora of personalities

For a long time, research into animal behavior was built on the view that individual differences are mostly raw material in the evolution of a species. Over time, natural selection should lead to animals that behave roughly the same, the thinking went, so that they make the best possible choices in every situation.

Then, in 2004, two influential papers — one led by Andrew Sih of the University of California, Davis, and the other led by Sasha R.X. Dall, then of the University of Cambridge — flipped that idea on its head. Rather than populations steadily evolving into behavioral monotony over time, the papers posed, variation between individual animals might itself be desirable for evolutionary success.

The papers drew on recent studies of mammals, birds, reptiles and even invertebrates such as mollusks, as well as the principles of game theory, the mathematical modeling of optimal strategies. Combined, the data support the idea that evolution can lead to consistent behavioral differences between members of the same species. That is, evolution gives rise to personalities.

“That got folks really excited,” says Kate Laskowski, a behavioral ecologist at UC Davis. Laskowski recalls an animal behavior conference in the early 2000s, in the wake of this revelation. “Every single talk was like, ‘Oh, we found personality in this animal, we found personality in that animal,’ ” she says. “That’s classic any time a new field starts.”

Personality is a big part of animal behavior, so the idea that it matters to conservation comes as no surprise to Daniel Blumstein. As a child, he attended events on the first Earth Day in 1970, and he has long been interested in bringing together animal behavior and conservation.

Now a behavioral ecologist at UCLA, Blumstein started his career studying how marmots in Pakistan’s Khunjerab National Park avoid predators. He became involved with local conservation groups and communities during his time there. It has taken time for the broader field of conservation biology to catch up on the importance of behavior, he says. “A lot of mainstream conservation is still population biology, population modeling, what makes populations go up and down,” Blumstein says. And “a lot of it is still genetics.”

“Individuality is one of those domains that people are exploring in some conservation contexts, and could be important in some.”

Daniel Blumstein
Behavioral ecologist at UCLA

When species reintroductions go wrong, though, it’s behavior that’s often to blame.

In a paper published in 2020, Blumstein and colleagues scrutinized 293 case studies of animals being released into the wild; 27.6 percent of them reported problems with behavior. The most common issues were related to movement, with animals traversing into areas they weren’t meant to go. When 12 endangered Hamilton’s frogs in New Zealand were moved 50 meters away to start a new population, for example, some of them immediately tried to head back home, a common problem in amphibian and reptile releases.

Other behavioral troubles noted by conservationists involved mating, finding food and, in some cases, behaviors tied to personality.

Boldness, a commonly studied personality trait, can have mixed effects on population health. Such was the finding of a 2013 study on reintroductions for two species of fox, the swift fox (Vulpes velox) and the Santa Catalina Island fox (Urocyon littoralis catalinae). When 31 captive-bred swift foxes were released onto the Blackfeet Indian Tribal Reservation in Montana, five of the 16 monitored foxes died. They were the boldest individuals, and they succumbed to dangers such as predators. By contrast, the reintroduced island foxes, with no natural predators, had more babies if they were bolder, and none of them died during the study period.

Similarly mixed benefits of boldness have been seen in released Blanding’s turtles and Tasmanian devils, both of which survived longer if they were more adventurous. But in blue-fronted parrots, shyer birds lived 40 days longer on average than bold ones.

For Naruto the ill-fated peccary, being asocial might have at first helped him avoid conflict with a bigger, stronger male. With a predator around, though, it would have paid for him to switch his behavior and become friendlier to gain protection from the group. But Naruto wasn’t keeping track of the optimal way to behave in every situation: He was just being himself.

Because Naruto and the other peccaries can’t do it all, the overall population can benefit from the mix of personalities that Nogueira identified — even if it means individuals make deadly mistakes.

How bridges influence behaviors

The study of animal personality has since matured and permeated fields such as evolution and community ecology. Behavior, including personality, is inseparable from conservation success any time it influences demographics, Blumstein says. Any behavior that affects an animal’s ability to survive, mate, raise offspring, move from place to place, avoid death and more can be of interest to conservationists.

Carlos Ruiz-Miranda, a conservation biologist at the State University of Northern Rio de Janeiro, rigorously tests personality in a conservation effort he’s involved in for a showy chickenlike bird called the black-fronted piping guan (Pipile jacutinga). Native to southeastern Brazil and parts of Paraguay and Argentina, these birds are classified as endangered by the IUCN due to habitat loss and illegal hunting.

“We use this test based on a human personality test,” Ruiz-Miranda says. The birds are scored on their sociability, aggression, acceptance of new foods, overall activity and whether they prefer to stay on the ground or hang out in trees. Like their chicken relatives, they sometimes scrounge around on the ground for food.

“We don’t want animals to do that a lot, because they’re very vulnerable to predators,” Ruiz-Miranda explains. He compared the testing process to a coach choosing a soccer or baseball player, when some attributes may be more important than others. For Ruiz-Miranda’s guans, the most important traits are being social, recognizing predators and not being ground foragers.

Ruiz-Miranda started his career with a long-running project to reintroduce endangered golden lion tamarins (Leontopithecus rosalia) into their native Brazil (see sidebar). After a rough start in the 1980s, that program became a roaring success once the introduced tamarins started reproducing — the babies were much more adjusted to their wild habitat than their captive-raised parents.

Now, changes to the monkey’s wild habitat are prompting the research team to take personality more seriously as a factor in their conservation.

The tamarin team recently built bridges to help the monkeys cross sections of the forest that have been clear-cut for oil and gas pipelines. Tamarins view these open areas with caution, fearing exposure to predators. Ruiz-Miranda noticed that some tamarin families cross the bridges readily, while others are more hesitant.

“We started thinking about these bridges being a filter of personalities,” he explains. So while the bridges allow tamarins to move around more easily, they may also be shaping the personality distribution of the entire population, which Ruiz-Miranda’s team is now studying further. The well-meaning bridges could be acting as a sieve, restricting areas of the forest to those tamarins who are brave enough to cross, with potential consequences for the group’s survival.

“Individuality is one of those domains that people are exploring in some conservation contexts, and could be important in some,” Blumstein says. But, he cautioned, “just because behavior is important doesn’t mean all of it’s important to solve any given problem.”

When testing is impossible

Of course, it’s not always possible to include detailed personality tests in reintroduction efforts. In December 2023, wildlife officials used darts to sedate 10 Oregon wolves from a helicopter hundreds of meters in the air, packed them up in crates and shipped them off to Colorado to start life anew.

“You try to isolate animals just based on how they respond to the helicopter, and you get what you can get,” says Eric Odell, the wolf conservation program manager at Colorado Parks and Wildlife who is leading the canines’ reintroduction into the state.

Personality has been studied in wolves before — at least as far back as 1972 — but mostly in captive individuals. Fully understanding the personalities of the Oregon wolves before capturing them would have taken intensive fieldwork. Figuring out how those personalities may influence the animals’ success when reintroduced would have taken even more research.

“I think the recognition that behavior is important is definitely becoming more relevant.”

Stewart Breck
Ecologist at the USDA National Wildlife Research Center

Though lacking in-depth personality info for the wolves, Oregon wildlife officials had a good understanding of who was who in each pack, Odell says. In a second capture-and-release in early 2025, 15 wolves were taken from British Columbia to join the others in Colorado. They had never been studied in any capacity before, aside from GPS collars the relocation team had fastened to some of the canines a month prior.

The reintroduction has been a bit rocky — so far, 10 of the wolves released into Colorado from Oregon and British Columbia have perished.

While it can be challenging for wildlife managers to add behavior and personality to their already full plates, it is becoming more appreciated as a crucial component of conservation.

“Most wildlife managers, they think about populations primarily,” says Stewart Breck, an ecologist at the U.S. Department of Agriculture National Wildlife Research Center in Fort Collins, Colo., who helps manage conflict between humans and carnivores like wolves and coyotes. “I think the recognition that behavior is important is definitely becoming more relevant.”

Breck sees two main areas where person­ality can play a key role in conservation: when an animal population is really small and “every individual is really important,” and when trying to mediate conflict between animals and people.

“Especially if you’re thinking about nonlethal techniques, then animal personality becomes a really critical factor,” Breck says. For example, fladry — ropes adorned with colorful flags that are hung around fences — are a popular tool for deterring wolves from preying on livestock. A bold wolf may not care about fabric flapping in the wind, while a shy wolf may be petrified.

Breck’s words would be music to Blumstein’s ears. In addition to working with conservationists throughout his career, he’s now part of a team working on a website interface designed to easily bring the science of conservation behavior to wildlife managers, as well as other knowledge they may lack.

“You might not be trained on how to run a focus group, to manage people or understand the people in your area,” Blumstein says. “You might not know how to identify stakeholders to figure out who should be consulted…. You might not know how to raise funds.”

With his new project, he says, “we’re really bringing the science and the social science and the management all together.”