Animals’ personalities can affect a species’ survival

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

Naruto was named after the main character from a popular manga and anime. He was the youngest male and one of the least social in his group of 17 peccaries. These piglike mammals were born and raised in captivity. They lived at the State University of Santa Cruz in Ilhéus, Brazil.

Researchers there planned to release the peccaries into two nature preserves in Brazil. But first, the peccaries were each given a personality test of sorts. They were video recorded as they went about their daily lives. Researchers collected 17 hours’ worth of data. They tallied aggressive actions, friendly touches and moments of exploration. The peccaries were ranked in traits such as boldness and friendliness.

The goal was to find out whether a peccary’s behavioral traits influenced its survival after release. White-lipped peccaries (Tayassu pecari) are at risk of extinction. They 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. Past efforts to reintroduce them had met limited success.

Around the globe, scientists are learning how an animal’s nature can affect its return to the wild.

For Naruto, being a loner may have been his undoing.

Naruto’s behavior stood out to Selene Nogueira. She studies animal behavior at the university and leads the 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. He had 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. Now, after about two years, the group has welcomed 10 babies. Nogueira concluded that peccaries need a mixture of character types to succeed in the wild. That includes solo adventurers like Naruto. But the group also needs social butterflies that stick together.

A century ago, scientists working in Brazil’s forests would have laughed at the idea of peccary personalities. But Nogueira’s work is part of a growing trend to use behavior research to guide conservation. And it’s become clear that personalities aren’t just for peccaries. They’re everywhere in the animal world.

Plenty of personalities

For a long time, scientists thought evolution would tend to make all animals of a species act roughly the same way. The thinking was: If there was a “best” way to act, animals that behave that way would survive. Over time, individual differences would disappear.

Then, in 2004, two influential papers flipped that idea on its head. The papers argued that having a variety of behaviors might actually help a species survive.

The papers drew on recent studies of mammals, birds, reptiles and even mollusks. They also used game theory, a type of math that finds the best strategies to do something. The data support the idea that evolution can lead to consistent behavior differences within a species. That is, evolution gives rise to personalities.

“That got folks really excited,” says Kate Laskowski. She is a behavioral ecologist at the University of California, Davis.

Personality is a big part of animal behavior. So the idea that it matters to conservation comes as no surprise to Daniel Blumstein. He has long been interested in bringing together the two fields.

Today, Blumstein is a behavioral ecologist at the University of California, Los Angeles. He started his career studying how marmots in Pakistan’s Khunjerab National Park avoid predators. While there, he got involved with local conservation groups. But many conservation studies still don’t account for behavior, he says.

Sometimes species reintroductions fail. Often behavior is to blame. In a paper published in 2020, Blumstein and colleagues studied 293 case studies of animals being released into the wild. More than a quarter of them reported problems with behavior.

The most common issues were related to movement. Animals sometimes crossed into areas they weren’t meant to go. In New Zealand, 12 endangered Hamilton’s frogs were moved 50 meters (160 feet) away to start a new population. But some of them immediately tried to head back home. This is a common problem in amphibian and reptile releases.

Other behavioral troubles involved mating and finding food. In some cases, the problems were tied to personality.

Boldness is a commonly studied trait. It can have mixed effects on population health. A 2013 study looked at two species of fox, the swift fox and the Santa Catalina Island fox. Researchers released 31 captive-bred swift foxes onto the Blackfeet Indian Tribal Reservation in Montana. Of the 16 foxes they monitored, five died. Those five were the boldest of the group. They were killed by predators and other dangers. By contrast, the island foxes had no natural predators. None of them died during the study period. And bolder island foxes had more babies.

Boldness had mixed results in other species, too. Blanding’s turtles and Tasmanian devils survived longer if they were more daring. But among blue-fronted parrots, shy birds lived 40 days longer on average than bold ones.

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

.cheat-sheet-cta {
border: 1px solid #ffffff;
margin-top: 20px;
background-image: url(“https://www.snexplores.org/wp-content/uploads/sites/3/2022/12/cta-module@2x-2048×239-1.png”);
padding: 10px;
clear: both;
}

Bridges and behaviors

The study of animal personality is now guiding some conservation efforts. Carlos Ruiz-Miranda is a conservation biologist at the State University of Northern Rio de Janeiro in Brazil. He tests personality in the black-fronted piping guan (Pipile jacutinga). This showy, chickenlike bird is native to southeastern Brazil and parts of Paraguay and Argentina. The IUCN classifies them as endangered. Habitat loss and illegal hunting are their main threats.

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

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

Early in his career, Ruiz-Miranda worked with golden lion tamarins (Leontopithecus rosalia). The goal was to return these endangered primates to their native Brazil (see sidebar). The program had a rough start in the 1980s. But it 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 the monkeys’ wild habitat is changing. This is prompting the research team to take personality more seriously. They see it as an important factor in the monkeys’ conservation.

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

“We started thinking about these bridges being a filter of personalities,” he explains. The bridges allow tamarins to move around more easily. But they may also be changing the mix of personality types in the population. The bridges could be screening out more timid tamarins. Only those brave enough to cross can access certain parts of the forest. This could affect the group’s survival. Ruiz-Miranda’s team is now studying this further.

When testing is impossible

Of course, it’s not always possible to include detailed personality tests in reintroduction efforts. In December 2023, wildlife officials sedated 10 Oregon wolves. They used darts shot from a helicopter hundreds of meters in the air. The team packed up the wolves in crates. Then they 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. Odell manages the wolf conservation program at Colorado Parks and Wildlife. He is leading the effort to bring the canines back to the state.

Personality has been studied in wolves before — at least as far back as 1972.  But most of the studies looked at captive wolves. Studying wild wolves takes a lot more time. And figuring out how their traits might affect the wolves’ success in Colorado? Even longer.

The Oregon wildlife officials lacked in-depth character info for the wolves. But they had a good understanding of who was who in each pack, Odell says.

In early 2025, another 15 wolves were taken from British Columbia. They joined the others in Colorado. These wolves had never been studied before. But the relocation team had fastened GPS collars to some of the canines a month prior.

The reintroduction has been a bit rocky. So far, 10 of those 25 wolves brought to Colorado have perished.

“Most wildlife managers, they think about populations primarily,” says Stewart Breck. He is an ecologist at the U.S. Department of Agriculture National Wildlife Research Center in Fort Collins, Colo. Breck 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. One is when an animal population is so small that each individual is important. The other is when trying to reduce conflict between animals and people.

When choosing strategies, “animal personality becomes a really critical factor,” Breck says. For example, fladry is a popular tool for keeping wolves away from livestock. These ropes adorned with colorful flags are hung on fences. A bold wolf may not care about fabric flapping in the wind. But a shy wolf may be petrified.

Wildlife managers have a lot on their plates. But more of them are seeing that personality matters. Understanding animals’ personality could help them choose which ones have the best chance of surviving. This could help bring back species at risk of extinction.