Wild birds with a lot of personality
By Carl Zimmer The New York Times
Thursday, March 3, 2005
A team of Dutch scientists is trying to solve the mystery of personality. Why are some individuals shy while others are bold, for example? What roles do genes and environment play in shaping personalities? And most mysterious of all, how did they evolve?
The scientists are carrying out an ambitious series of experiments to answer these questions. They are studying thousands of individuals, observing how they interact with others, comparing their personalities to their descendants' and analyzing their DNA.
It may come as a surprise that their subjects have feathers. The scientists, based at the Netherlands Institute of Ecology, are investigating personalities of wild birds.
Until recently, most experts in personality would have considered such a study as nothing but foolish anthropomorphism. "It's been looked at with suspicion and contempt," said Samuel Gosling, a psychologist at the University of Texas.
But scientists have found that in many species, individual animals behave in consistently different ways. They argue that these differences meet the scientific definition of personality.
If they are right, then human personality has deep evolutionary roots. "It's a matter of degree, not of differences," said Piet Drent of the Netherlands Institute of Ecology.
The bird study that Drent and his colleagues are conducting is considered the most ambitious investigation of personality in wild animals. "They've gone the furthest," said Sasha Dall, an evolutionary biologist at the University of Exeter in Cornwall.
The Dutch researchers are studying the importance of genes to the personalities of the birds and the effect different personalities have on their survival. They hope next to carry out parallel studies in humans to see whether the same forces behind the evolution of bird personalities are at work in our own species.
The science of human personality is about a century old.
Psychologists have relied largely on questionnaires and other testing methods to map out its dimensions. One common method is for scientists to ask their subjects how well certain adjectives apply to themselves (or to people they know well).
"Certain traits tend to go together," Gosling said. "We find that people who are energetic also tend to be talkative. It needn't be that way, but that's how it tends to be." The flip side is true as well: Less energetic people tend to be less talkative.
Psychologists have found they can bundle these traits into just a few personality dimensions. People may be more or less extroverted, for example, which means they are sociable, assertive and tend to have positive emotions. The same dimensions have been documented across the world, from Zimbabwe to the Russian Arctic, suggesting that they are universal in humans.
Some studies have suggested that genes are responsible for some of the differences in people's personality ratings. But they have been far from conclusive because scientists cannot do experiments with humans. "Human mothers will not let you just swap their infants at birth, which would be a great study to do," Gosling said.
It has been only in the last decade or so that scientists have investigated whether animals have personalities. In one pioneering study in the mid-1990s, Gosling studied a colony of 34 hyenas at the University of California, Berkeley. "My goal was simply to say, can we measure personality in animals? It wasn't clear it was going to work," he said.
Gosling asked the four caretakers of the colony to fill out a modified version of the human questionnaire for each animal.
"It turned out that they agreed at the level you find in humans," Gosling said. What's more, the hyena personalities fit some of the dimensions found in humans, like neuroticism and agreeableness. Since then, a number of other studies have documented personalities in animals, from chimpanzees to squid.
To some biologists, the main question about these animal personalities is why natural selection keeps such a wide range of them. "Why hasn't one personality become the standard in the population?" asked Drent. If being extroverted offers the best odds for a hyena to reproduce, you might expect that over time, all hyenas would wind up as extroverts.
Drent and his colleagues hope that their study on birds may reveal some clues. They are studying a European relative of chickadees called the great tit (Parus major). Most of the birds spend their entire lives in a single forest, and they are happy to move into comfortable nest boxes provided by the scientists. As a result, the Dutch researchers can track the entire population of birds for years, keeping tabs on their health and their success at reproducing.
The scientists can also bring some of the birds into the lab in order to measure their personalities or carry out breeding experiments.
"These birds are perfect for these sorts of studies," said Niels Dingemanse of the University of Groningen, a collaborator with Drent. Instead of questionnaires, the Dutch team tests the behavior of the birds to measure their personalities. In one test, the scientists place a strange object - a penlight battery or a Pink Panther doll - in a bird's cage. Some birds are quick to approach it, while others hang back.
In another experiment, the researchers open a cage door, allowing the birds to explore a large room filled with five artificial trees.
Some birds are quick to explore the trees, while others prefer to remain in the comforts of their cage.
In a third experiment, the researchers place a bowl of tasty mealy worms in the room. When the birds land on the bowl to eat, the researchers startle the birds by lifting up a nearby metal plate. They then see how much time passes before the bird returns to the bowl.
The tests revealed that the birds have consistent personalities that remain stable for years. Bold birds, as the scientists call them, are quick to inspect new objects, to explore the trees and to recover from the metal plate surprise.
Shy birds are slow on all three counts. The differences go well beyond these tests. Bold birds are also more aggressive than shy ones and experience less stress when the scientists handle them.
Breeding experiments revealed that these traits had a strong genetic basis. Over just four generations, the researchers could produce significantly bolder and shyer birds.
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