Other scientists have found evidence in the wild that is compatible with that laboratory work. Max Wolf, a theoretical biologist at the University of Groningen in the Netherlands and lead author of the study in Nature notes that birds in his country, including oystercatchers, can either breed early or hold off until later, and that decision is a personality trait that is handed down from one generation to the next.
Van Doorn said researchers in the Netherlands have studied the personalities of a small bird, the great tit, over successive generations.
"They had the birds in aviaries and they tested individuals for their boldness or their shyness," van Doorn said. "The boldest were allowed to reproduce, and in the course of generations the difference (between the bold and the shy birds) increased, and this is usually an indication that there is a genetic component."
It's all a bit "puzzling," he added, because a risky personality leads to risky behavior in many unrelated activities. A hawk that will torment smaller birds is also likely to challenge an eagle.
"There are examples where you can see this rigidity in a personality is not always a very good thing," he said. "There are studies of spiders, for example, where some spiders are more aggressive than others when they defend their territories. But those spiders are also more aggressive to their own offspring. Sometimes, they eat them."
Other studies have shown that animals are more like people than was once thought, at least in terms of personalities. Members of the same species that are about the same age and size and sex can behave vary differently, even under similar circumstances.
That is counter intuitive, at least from an evolutionary standpoint. It indicates that even birds can be very rigid in their behavior, and that's not always the best policy. Even for an aggressive and fearless animal, sometimes its better to run.