At parties, it’s hard to miss the loud and extroverted types, those eager to join in any games, songs, or dances, while more reserved souls are likely to hang back, outside the spotlight.

Ongoing research into animal personalities—from insects to songbirds, from octopuses to primates—has revealed similar divisions: Shy and bold individuals exist within every population.

Such differences can affect an animal’s survival. In some situations, it pays to be adventurous when seeking food and mates. In several species, including zebrafish, being bold makes an individual more successful in finding a mate and reproducing. Other times, being shy is less risky for reproduction—and leaves behind more progeny.

Now a scientist has reported the first discovery of bold and shy personalities among a wild population of bottlenose dolphins in Italy’s Gulf of Aranci.

Bold dolphins may be particularly useful to their group, for instance when it comes to finding food. Such outgoing individuals can help spread important social information among the group, such as knowledge about feeding opportunities.

“We’d known that dolphins have these personalities from captive studies, but that is not their normal lives,” says Bruno Díaz López, a behavioral ecologist at the Bottlenose Dolphin Research Institute in Pontevedra, Spain, and author of the new research. “Now, we know wild dolphins have personalities, and that these are important in their social system—as they are in ours.”

What’s more, his analysis reveals the more gregarious dolphins had stronger social relationships than shyer ones—something researchers have shown in other species, but only under controlled conditions, such as fish in an aquarium.

“The study should be applauded for demonstrating these expected links in real life, where getting the data is super-challenging,” says Orr Spiegel, a behavioral ecologist at Tel Aviv University who wasn’t involved in the study. (Read more about dolphin intelligence.)

Strong personalities

Scientists have been studying bottlenose dolphins in the Gulf of Aranci for 16 years as part of a long-term study of the marine mammals. Unlike an orca pod or baboon troop, which live in stable groups, dolphins live in what are called “fission-fusion societies.” Individuals come and go; the average group size is four, but some may be as large as 30.

In the Gulf of Aranci, dolphins regularly interact with fishermen, tourists, and staff of a local fish farm, giving Díaz López a prime opportunity to assess their personalities in action.

By analyzing a thousand photos of the Gulf of Aranci dolphins, he identified 24 adult individuals—13 females and 11 males—that had been observed multiple times.

Scientists typically equate an animal’s shyness or boldness with its response to novel, risky, or challenging situations. An animal with a bold personality, for instance, is more likely to approach a novel object or investigate a potential predator than is one that is shy. (Read how dolphins have “names.”)

For the next step in his experiment, Díaz López filmed the reaction of these 24 dolphins to two new threats: the presence of a person in snorkeling gear and the activation of an underwater alarm, designed to deter dolphins from fishing nets.

Between 2004 and 2011, Díaz López performed 192 such tests (96 in the presence of the alarm; 96 in the presence of a snorkeler).

He then reviewed each film clip and measured the distance between the dolphin and the new threat, according to the study, published in the May issue of Animal Behaviour.

He found some individuals were consistently very bold—that is, they were willing to closely approach both a strange device emitting an obnoxious sound and a strange person. He also observed dolphins that were consistently shy, that stayed approximately 220 feet away on average, and others that were consistently intermediate in their reactions—sometimes approaching, sometimes avoiding the stimulus.

Watch wild dolphins help fishermen—and get a reward Study finds a tight social bond among dolphins that hunt fish alongside fishermen.

Mauricio Cantor, National Geographic Grantee

The consistency of the bold dolphins in approaching the objects and the shy dolphins in avoiding them is “remarkably high,” Andy Sih, a behavioral ecologist at the University of California, Davis, said by email.

“These dolphins showed a much stronger, clearer signal of personality differences than has been seen in almost any other of the hundreds of studies done on animal personalities,” says Sih, who studies animal personalities.

Family connectors

Díaz López also observed which of the other dolphins his 24 study subjects spent time with, and from these relationships, he built a model of their social networks.

The analysis shows that these associations vary according to personality type. Bolder dolphins showed deeper social connections, such as a stronger preference for spending time with certain individuals (although not necessarily with other bold dolphins) than the shy animals. Female and male dolphins were equally bold or shy. (Learn more about what animals may really be thinking.)

As in other studies, these differences in social behavior could affect individual dolphins’ reproductive success by building cooperative alliances—particularly among males in other groups.

Because bold dolphins spend most of their time with other dolphins, these animals, he concludes, may have a significant role in keeping their groups intact.

Why be bold or shy?

Like most animal personality studies, this one does not address an intriguing, unsettled question: Why? “It’s a great, solid study,” says Sasha Dall, a behavioral ecologist at the University of Exeter in the United Kingdom.

“But why is there personality in dolphins or any species? There’s no evolutionary reason to think every species should have shy and bold individuals.”