Parrots are talkative birds, with impressive, humanlike linguistic abilities. Also like us, male and female parrots are lifelong vocal learners. Because of these similarities, researchers have long wondered whether parrot chicks learn their first calls or if these sounds are innate. For the first time, scientists have succeeded in studying the calls of parrot chicks in the wild. They find that the birds do learn their first calls—and from their parents, much as human infants do. The findings suggest that parrots may be better than songbirds as models for studying how humans acquire speech.
Like other parrot species, green-rumped parrotlets (Forpus passerinus), a parakeet-sized species that lives in South America, make what scientists term a signature contact call, a sound that functions much like a name. The birds use it to find and recognize mates and identify their chicks. Other studies have shown that wild parrots often imitate one another's contact calls—rather like someone calling out the name of a friend. "One study of another species of captive parrotlets suggested that individual birds are assigned names by their family members," says ornithologist Karl Berg of Cornell University.
But he wanted to know whether the birds do this in the wild, too, and why. Captive studies cannot, by themselves, explain what function such behaviors serve in nature or how they evolved. But studying parrots in the wild is "extremely difficult" because they generally nest in hollows high in trees, says behavioral ecologist Timothy Wright of New Mexico State University in Las Cruces, an expert on wild parrots.
To get around this problem, Berg and his colleagues worked with a wild population of green-rumped parrotlets in Venezuela that has been studied since 1987. The parrotlets nest in hollows in fence posts, and scientists set out 106 artificial nesting boxes, which the parrotlets readily moved into. The boxes allowed the researchers to access the birds, eggs, and chicks and to record audio and video in the nests. For 24 years, the researchers have tracked thousands of parrotlet pairs and chicks, so they know the birds' family trees.
Berg and colleagues swapped clutches of eggs between 12 unrelated pairs of parrotlets. When the chicks hatched, they were raised by foster parents. Serving as a control were chicks in eight other nests that lived with their biological parents. If the chicks' contact calls are innate, they should resemble those of the biological parents rather than those of the foster parents.
The team recorded and analyzed the calls made by the biological and foster parents and by the nestlings. The analysis, reported online today in the Proceedings of the Royal Society of London B, shows that the chicks learn their calls from the parents that raised them; calls are not inherited. "The parents—both mom and dad—provide a template," which the nestlings change slightly so that each chick ends up with a unique call, Berg says.
Later, when the chicks leave their nests, their parents use the contact calls to find their youngsters because they must be fed for another 21 days. Fledged chicks roost in large groups, so the parents need some means of identifying their own offspring, Berg explains.
The study is "an exciting first step in unraveling why parrots match each others' calls in the wild," Wright says. "It's a very cool study," adds Ofer Tchernichovski, a biopsychologist at Hunter College in New York City. The work "raises the possibility that parrots may be acquiring their calls in a way that's different from other species and might even be similar to some aspects of speech learning in human infants."