Animal personalities can play an important role in saving species

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

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

Intended to be reintroduced to the Estação Veracel private natural heritage reserve in Brazil and the Pau-Brasil ecological station, the peccaries were each subjected to a sort of personality test by researchers at the laboratory. The pig-like mammals were videotaped as they went about their daily lives, yielding 17 hours of behavioral data. Their aggressive actions, friendly contacts and moments of exploration were tallied so that peccaries could be classified according to traits such as boldness and sociability.

The aim was to determine whether a peccary’s behavioral traits influenced its survival once released into the wild. White-lipped peccary (Tayassu peccary) are listed as vulnerable by the International Union for Conservation of Nature, or IUCN. In Brazil, the size of the species’ historic range fell by 60% in 2020, and past efforts to reintroduce it have met with limited success.

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

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

Naruto’s behavior struck Selene Nogueira, an ethologist at the university and head of the laboratory’s peccary project. “He was the last to eat and so he was thinner than the others,” Nogueira explains. “I think his personality was a little shy.” Once the peccaries were released, Naruto continued his antisocial habits. His wanderings helped the group disperse. But less than a year after his release, researchers found him limping with deep bite marks, likely from a jaguar or puma. He died three days later.

Peccaries are known for repelling predator attacks in groups. Sure enough, the rest of the peccaries fared better and now, after about two years, the group has welcomed 10 babies. From his study, Nogueira generally concluded that for a group of loose peccaries to succeed, they need a mix of personality types: antisocial adventurers to go off and push the group, as Naruto did, and social butterflies who stay 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 over the past two decades showing that personalities aren’t just the preserve of peccaries: They’re present everywhere in the animal world.

A multitude of personalities

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

Then, in 2004, two influential newspapers…one directed by Andrew Sih from the University of California, Davis, and the other directed by Sasha RX Dallthen of Cambridge University – turned that idea on its head. Rather than populations gradually evolving toward behavioral monotony over time, the papers suggest, variation among individual animals might itself be desirable for evolutionary success.

The articles draw on recent studies of mammals, birds, reptiles and even invertebrates such as molluscs, as well as the principles of game theory, the mathematical modeling of optimal strategies. Together, the data support the idea that evolution can lead to consistent behavioral differences between members of the same species. In other words, evolution gives rise to personalities.

“It really got people excited,” says Kate Laskowski, a behavioral ecologist at UC Davis. Laskowski remembers attending an animal behavior conference in the early 2000s, following this revelation. “Every conversation was like, ‘Oh, we found personality in this animal, we found personality in this animal,’” she says. “It’s classic every time a new field starts.”

Personality plays an important role in animal behavior, so the idea that it is important for conservation comes as no surprise to Daniel Blumstein. As a child, he attended the events of the first Earth Day in 1970 and has long been interested in the connection between animal behavior and conservation.

Now a behavioral ecologist at UCLA, Blumstein began 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 took time for the broader field of conservation biology to catch up on the importance of behavior, he says. “A lot of the conservation concerns remain about population biology, population modeling, what makes populations increase and decrease,” Blumstein says. And “much of this is still genetic.”

However, when species reintroductions fail, it is often behavior that is to blame.

In a paper published in 2020, Blumstein and colleagues examined 293 case studies of animals released into the wild; 27.6 percent of them reported behavioral problems. The most common problems were related to movement, with animals crossing areas where they were not supposed to go. When 12 in danger Hamilton’s frogs in New Zealand were moved 50 meters away to create a new population. For example, some of them immediately tried to return home, a common problem during amphibian and reptile releases.

Other behavioral disorders noted by conservationists involved mating, foraging, and, in some cases, personality-related behaviors.

Audacitya commonly studied personality trait, may have mixed effects on population health. Such was the discovery of a 2013 study on reintroductions of two fox speciesthe swift fox (A fast fox) and the Santa Catalina Island fox (Urocyon littoralis catalinae). When 31 captive-bred swift foxes were released on the Blackfeet Indian Tribal Reservation in Montana, five of the 16 monitored foxes died. They were the boldest individuals and succumbed to dangers such as predators. In contrast, reintroduced island foxes, without natural predators, had more babies if they were bolder, and none of them died during the study period.

Similar benefits of boldness were observed in released Blanding’s turtles and Tasmanian devils, both of which survived longer if they were more adventurous. But among blue-fronted parrots, the shyest birds lived an average of 40 days longer than the bolder birds.

For Naruto, the hapless peccary, being antisocial might have initially helped him avoid conflict with a larger, stronger male. With a predator around, however, it would have paid for it to change its behavior and become more friendly to protect itself from the group. But Naruto wasn’t monitoring the optimal way to behave in each situation: he was just being himself.

Because Naruto and the other peccaries can’t do everything, the population as a whole can benefit from the mix of personalities Nogueira identifies – even if it means individuals make deadly mistakes.

How bridges influence behavior

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 whenever it influences demographics, Blumstein says. Any behavior that affects an animal’s ability to survive, mate, raise offspringmoving from place to place, avoiding death and much more may be of interest to conservationists.

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

“We use this test based on a human personality test,” says Ruiz-Miranda. 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 scavenge on the ground for food.

“We don’t want animals to do this too often, because they are very vulnerable to predators,” says Ruiz-Miranda. He compared the testing process to that of a coach choosing a football or baseball player, when some attributes may be more important than others. For Ruiz-Miranda guans, the most important traits are being social, recognizing predators, and not feeding on the ground.

Ruiz-Miranda began her career with a long-term project to reintroduce golden lion tamarins és, an endangered species (Leontopithecus rosalia) in their native Brazil (see box). After a rocky start in the 1980s, this program became a great success once the introduced tamarins began to reproduce: the babies were much more adapted to their wild habitat than their captive-bred parents.

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

THE tamarin team recently built bridges to help monkeys cross sections of 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 bridges with ease, while others are more hesitant.

“We started thinking about these bridges as a filter of personalities,” he explains. So while the bridges allow tamarins to move more easily, they could also shape the personality distribution of the entire population, something Ruiz-Miranda’s team is now studying in more depth. These well-intentioned bridges could act as a sieve, limiting certain areas of forest to the tamarins brave enough to cross them, with potential consequences for the survival of the group.

“Individuality is one of those areas that people explore in some conservation contexts, and might be important in some contexts,” says Blumstein. But, he cautions, “just because behavior is important doesn’t mean it’s important to solve a given problem.”

When testing is impossible

Of course, it is 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 feet in the air, packed them into crates and shipped them to Colorado to start their lives again.

“You try to isolate animals just based on their reaction to the helicopter, and you get what you can get,” Er says. IC Odell, wolf conservation program manager at Colorado Parks and Wildlife, who is leading the state’s reintroduction of dogs.

The personality was previously studied in wolves– at least since 1972 – but mainly in captive individuals. Fully understanding the personalities of Oregon wolves before capturing them would have required intensive fieldwork. Understanding how these personalities may influence the animals’ success upon reintroduction would have required even more research.

Although they lacked detailed information about wolves’ personalities, 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 captured in British Columbia to join the others in Colorado. They had never been studied in any capacity before, aside from the GPS collars the relocation team had attached to some canines a month before.

The reintroduction has been a bit difficult: So far, 10 of the wolves released into Colorado from Oregon and British Columbia have perished.

Although it can be difficult for wildlife managers to add behavior and personality to their already full plates, it is increasingly appreciated as a crucial part of conservation.

“Most wildlife managers think about populations first,” says Stewart Breck, an ecologist at the U.S. Department of Agriculture’s National Wildlife Research Center in Fort Collins, Colo., who helps manage conflicts between humans and carnivores like wolves and coyotes. “I think the recognition of the importance of behavior 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 “each individual is really important”, and when it tries to mediate conflicts between animals and humans.

“Especially if you’re considering non-lethal techniques, animal personality becomes a really critical factor,” says Breck. For example, fladry – ropes decorated with colorful flags hung around fences – are a popular tool to deter wolves from preying on livestock. A bold wolf may not care about fabric flapping in the wind, while a timid wolf may be petrified.

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

“You may not be trained in how to lead a focus group, how to manage people, or how to understand people in your area,” Blumstein says. “You may not know how to identify stakeholders to determine who should be consulted… You may not know how to raise funds.

With his new project, he says, “we are really bringing together science, social science and management.”

Brazilian monkeys offer early lessons in conservation

Current work aimed at understanding animal personalities builds on an earlier push by conservationists to consider behavior in general. For a classic example of the importance of behavior for conservation, UCLA’s Daniel Blumstein cites golden lion tamarins.

If you walked through Rock Creek Park in Washington, D.C., in the early 1990s, you might have come across a troop of free-roaming monkeys with brilliant orange fur and long, twiggy fingers. The Smithsonian National Zoo has released endangered golden lion tamarins (Leontopithecus rosalia) in a part of the zoo grounds connected to the park, making the world the oyster of primates.

“Tamarins had the flexibility to go wherever they wanted within the city of Washington, D.C., or beyond,” says Carlos Ruiz-Miranda, a conservation biologist at Northern State University in Rio de Janeiro. “They could have gone all the way to Baltimore.”

Tamarins released at the National Zoo and other zoos around the country did not take up permanent residence. They were in training and eventually released back to their native Brazil, as part of a long-term effort to save the species from extinction. The monkeys were fitted with radio collars to facilitate tracking and were constantly monitored by zoo staff.

Golden lion tamarins are native to Brazil’s Atlantic Forest, which has been subject to clear-cutting and development since Portuguese colonizers first set their sights on it in 1500. The late Brazilian biologist Adelmar Coimbra-Filho realized the tamarins were in trouble in the 1960s after wandering through the Atlantic Forest and having difficulty finding them. He began attempting to breed them in captivity in 1962, hoping to reintroduce them into the wild.

But his efforts, as well as those of other early captive breeding efforts, did not yield good results. Despite their undeniable charisma, wild golden lion tamarins have been little studied: scientists simply didn’t know enough about them to breed them successfully.

“For any reintroduction program, you need to know some basic things about the animal,” says Ruiz-Miranda, who joined the National Zoo’s tamarin project in 1992. “And tamarins were a big surprise to everyone at first.”

Most group-living primates are polygamous, meaning that males mate with multiple females. But when male tamarins were housed with several unrelated females, the females spent more time fighting with each other than mating with the male. It turns out that golden lion tamarins are generally monogamous, with males and females mating exclusively.

“You have to keep them in pairs,” says Ruiz-Miranda. Once researchers figured this out, the tamarins began to reproduce.

In 1984, captive-born tamarins were introduced into and around the Poço das Antas Biological Reserve, a protected area created by Coimbra-Filho and fellow Brazilian conservationist Alceo Magnanini.

It didn’t go very well. Fourteen tamarins were released in this first attempt, and only five monkeys remained after eight months.

The problem is that tamarins tend to live in traditional nuclear families consisting of a mother, father and their offspring. Both parents help raise the babies, including teaching them to use their long fingers to fish out tasty insects from nooks and crannies. Learning is key: Tamarins are not born knowing how to survive in the wild.

The resounding failure in 1984 prompted scientists to let the tamarins roam free in the United States for a few months before heading to Brazil. More captive-born tamarins were introduced to Brazil between 1984 and 2000, and two-thirds of them died within two years. Some were captured by jungle cats. Some were bitten by snakes or stung by bees. Many died of starvation.

It turned out that tamarins that had previously trained by roaming freely in American parks don’t fare any better than the tamarinds that didn’tleading the researchers to conclude that the monkeys needed a longer training period before being integrated into the big leagues.

All this effort finally paid off. A 2023 census in Brazil revealed 4,800 wild tamarins, of which more than 2,500 were descended from reintroduced pioneers.

Beyond bringing more tamarins into the world, the project showed the importance of taking animal behavior into account when trying to save a species.