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The personality of an animal plays a big role in whether it can survive in the wild. While scientists have always known that nature matters, they have only recently focused on how individual personalities affect a species' future. A perfect example involves a white-lipped peccary named Naruto. Much like the ninja character from a popular cartoon, Naruto was a loner. He was the youngest male and one of the least social animals in his group. This group of 17 pig-like mammals was born and raised in a zoo at the State University of Santa Cruz in Ilhéus, Brazil. Scientists planned to release these peccaries into two nature preserves to help the wild population grow.
Before the release, the researchers tested the personality of each animal. They recorded 17 hours of video showing the peccaries' daily lives. During this time, they counted aggressive actions, friendly touches, and moments of exploration. Each peccary was ranked for traits like boldness and friendliness. The goal was to see if an animal's behavior influenced its chances of surviving after being released. White-lipped peccaries are at risk of extinction. They are listed as vulnerable by the International Union for Conservation of Nature (IUCN). By 2020, the area where these animals once lived in Brazil had shrunk by 60 percent. Past attempts to reintroduce them had seen limited success.
For Naruto, his solitary personality may have led to his end. His behavior stood out to Selene Nogueira, who studies animal behavior. "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." After the peccaries were released, Naruto continued his lonely ways. His wanderings did help the group spread out. However, less than a year later, researchers found him limping. He had deep bite marks, likely from a jaguar or puma. He died three days later.
Peccaries are known to fight off predators when they are in a group. The rest of the peccaries did indeed fare better. After about two years, the group has welcomed 10 new babies. Nogueira concluded that peccaries need a mix of personality types to succeed in the wild. That includes solo adventurers like Naruto, but the group also needs very social animals that stick together.
A century ago, scientists might have laughed at the idea of peccary personalities. But Nogueira's work is part of a growing trend. More and more, behavior research is being used to guide conservation efforts. It is now clear that personalities exist throughout the animal world.
For a long time, scientists thought evolution would make all animals of a species act in roughly the same way. The thinking was that if there was a "best" way to act, animals behaving that way would survive. Over time, individual differences would disappear. Then, in 2004, two influential papers changed that idea. The papers argued that having a variety of behaviors might actually help a species survive. They drew on studies of mammals, birds, reptiles, and even mollusks. The data support the idea that evolution can lead to consistent behavior differences within a species. In other words, evolution gives rise to personalities.
"That got folks really excited," says Kate Laskowski, a behavioral ecologist at the University of California, Davis. Personality is a big part of animal behavior. Daniel Blumstein, a behavioral ecologist at UCLA, has long been interested in connecting behavior and conservation. He says many conservation studies still do not account for behavior. Sometimes species reintroductions fail. Often, behavior is the reason. In a 2020 paper, Blumstein and colleagues studied 293 cases of animals being released into the wild. More than a quarter reported problems linked to behavior.
The most common issues were related to movement. Animals sometimes went into areas they were not supposed to. In New Zealand, 12 endangered Hamilton's frogs were moved about 50 meters to start a new group. But some immediately tried to return home. This is a common problem when releasing amphibians and reptiles. Other behavioral troubles involved mating and finding food. In some cases, the problems were tied to personality.
Boldness is a trait scientists often study. It can have mixed effects on a population's health. A 2013 study looked at two fox species. Researchers released 31 captive-bred swift foxes in Montana. Of the 16 foxes they tracked, five died. Those five were the boldest of the group. They were killed by predators and other dangers. In contrast, a study of island foxes, which have no natural predators, found that bolder foxes actually 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 peccary, being asocial might have helped him at first. He could avoid conflict with a bigger, stronger male. But with a predator around, it would have been better for him to change his behavior. Rejoining the group could have protected him. Naruto wasn't thinking about the best strategy for each situation. He was just being himself.
The study of animal personality is now guiding some conservation work. Carlos Ruiz-Miranda is a conservation biologist in Brazil. He tests the personality of the black-fronted piping guan. This showy, chickenlike bird is native to parts of South America. 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 also rates their acceptance of new foods and overall activity. Like chickens, guans sometimes search 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." 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. The goal was to return these endangered primates to their native Brazil. The program had a rough start, but it became very successful once the tamarins started having babies. Now the monkeys' forest habitat is changing. Parts of it have been cleared for oil and gas pipelines. Tamarins are cautious of these open areas because they fear predators. The research team recently built bridges to help the monkeys cross these dangerous sections. Ruiz-Miranda noticed that some tamarin families cross the bridges easily. Others are more hesitant.
"We started thinking about these bridges being a filter of personalities," he explains. The bridges let tamarins move 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 the brave ones can access certain parts of the forest. This could affect the group's long-term survival. Ruiz-Miranda's team is now studying this further.
Of course, it is not always possible to give detailed personality tests before releasing animals. In December 2023, wildlife officials used a helicopter to sedate 10 wolves in Oregon. They packed the wolves in crates and shipped them to Colorado to start a new life.
"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. Personality has been studied in wolves before, but most studies looked at captive wolves. Studying wild wolves takes far more time. The Oregon officials did not have deep personality information for the wolves they moved. But they did understand the social structure of each pack, Odell says. In early 2025, another 15 wolves were taken from British Columbia to join the others in Colorado. These wolves had never been studied before. The reintroduction has had some challenges. So far, 10 of the 25 wolves brought to Colorado have died.
"Most wildlife managers, they think about populations primarily," says Stewart Breck. He is an ecologist who helps manage conflicts between humans and carnivores like wolves. "I think the recognition that behavior is important is definitely becoming more relevant." Breck sees two main areas where personality is key for conservation. One is when an animal population is so small that every single individual matters. 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, a tool called fladry uses ropes with colorful flags to keep wolves away from livestock. A bold wolf may ignore the flags flapping in the wind. But a shy wolf may be terrified of them.
Wildlife managers have many responsibilities. But more of them are starting to see that personality matters. Understanding animal personalities could help them choose which individuals have the best chance of surviving. This knowledge could be crucial for bringing back species that are at risk of disappearing forever.