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Listen to part of a lecture in an animal behavior class.

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(female professor) Okay, we\'ve been talking about bird communication, uh, their songs and calls. Can anyone remind us of the differences between the two?

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(male student) Well, bird songs are usually produced only by males and they\'re used to attract mates or to stake out territory.

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But both males and females produce calls, which are used for things like warnings or begging for food.

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(female professor) Right, and is there anything else?

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(female student) Yeah. Male birds learn their songs when they\'re young, but calls are usually instinctive. They\'re genetically programmed, not learned.

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(female professor) Good. Now some birds that don\'t even produce songs are great imitators. Right?

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Think about members of the psittacines family commonly referred to as parrots.

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Psittacines comprise nearly 400 species, including true parrots, parakeets, macaws, cockatoos and so on.

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In captivity, they mimic human speech, but we don\'t really understand why, what purpose would this trait, this ability to mimic sound so accurately serve them in the wild.

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To answer that we must look at how parrots communicate in the wild.

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Like I said unlike other bird species, parrots don\'t produce songs, they produce only calls.

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And studies suggest that unlike most other birds, the parrots’ calls aren\'t genetically programmed, but learned and that they continue to learn new calls throughout their lives.

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Let\'s look at a recent study about parrot communication.

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(male student) I read it\'s difficult to study parrots because they roost high up in the trees. And the males and females look really similar.

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(female professor) Yes. And many species have beaks, strong enough to tear off those bands——researchers put on birds\' legs to identify them.

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But there have been a few studies of parrot communication, including the one we\'ll discuss today.

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But first, some background, in the 1980s, a researcher who was studying birds on a cattle ranch in Venezuela noticed several small psittacines called parrotlets who were nesting inside hollow spaces in the fence posts.

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He wondered if he could make artificial nesting boxes that would appeal to these parrotlets. So, he designed some and eventually ended up with over 100 nests.

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Researchers have been studying the parrotlets there ever since. This research has yielded a wealth of data about parrot behavior and life histories.

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(female student) So, the nesting boxes made this type of parrots easier to study?

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(female professor) Right. Also, unlike most psittacines, males and females are easily distinguishable, plus they tolerate being handled by researchers. These parrotlets even leave their leg bands alone.

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The studies followed more than 8,000 parrotlets throughout their lives, keeping track of all sorts of things, such as who\'s related to whom.

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So, when ornithologist Carl Berg wanted to study communication between parrot parents and their nestlings in the wild, he had the perfect place to do it.

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(male student) Okay, so here communication means calls, and most birds make a lot of different calls, right? What kind did Berg want to study?

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(female professor) He was interested in what we call a contact call, the most basic call. To us, a contact call sounds like a few simple peeps.

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But researchers have proposed that these calls are like the parrots’ names.

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And what Berg wanted to do was find out if these contact calls were learned behaviors or instinctual.

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What he did was this: first, he swapped eggs among 9 nests so that some sets of chicks were raised by unrelated parrots like foster parents. He left 8 other nests untouched as controls.

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Then he made weekly video and audio recordings inside the nests after the chicks hatched. And he made recordings outside the nest when the parents came and went.

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Now the sounds are too fast for us to be able to hear the differences.

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So, Berg converted them into spectrograms or pictures of the sounds. Then he analyzed the spectrograms using computer programs that search for similarities.

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Interestingly, he found that the parents provide a basic call template to the chick at about 3 to 4 weeks, which each chick learns and slightly modifies to make its own contact call, its own name.

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He also found that calls of nestlings are more similar to the calls of their primary caregivers, the foster parents than to any other adults, even their biological parents.

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And this similarity helps parents recognize their nestlings after they\'ve left the nest.

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(male student) Why do they need to recognize each other?

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(female professor) Because parrotlets parents continue to feed their fledglings for about 3 weeks after they\'ve left the nest.

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Since fledglings roost in large groups, parents have to be able to find them. And Berg believes that they do so using those calls.

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(female student) So, but what exactly does this have to do with why parents in captivity mimic human voices?

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(female professor) Ah. See, Berg discovered that the nestlings not only create and learn their own names, they learn each other\'s names as well.

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Just as the parents have to learn each individual fledgling’s name in order to find them after they\\\\\\\'ve left the nest.

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So, we have the first verified explanation for why mimicry is so important to psittacines in the wild.

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