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1 .Listen to part of a lecture in an animal behavior class.
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2 .(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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3 .(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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4 .But both males and females produce calls, which are used for things like warnings or begging for food.
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5 .(female professor) Right, and is there anything else?
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6 .(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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7 .(female professor) Good. Now some birds that don\'t even produce songs are great imitators. Right?
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8 .Think about members of the psittacines family commonly referred to as parrots.
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9 .Psittacines comprise nearly 400 species, including true parrots, parakeets, macaws, cockatoos and so on.
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10 .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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11 .To answer that we must look at how parrots communicate in the wild.
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12 .Like I said unlike other bird species, parrots don\'t produce songs, they produce only calls.
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13 .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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14 .Let\'s look at a recent study about parrot communication.
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15 .(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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16 .(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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17 .But there have been a few studies of parrot communication, including the one we\'ll discuss today.
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18 .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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19 .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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20 .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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21 .(female student) So, the nesting boxes made this type of parrots easier to study?
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22 .(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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23 .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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24 .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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25 .(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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26 .(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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27 .But researchers have proposed that these calls are like the parrots’ names.
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28 .And what Berg wanted to do was find out if these contact calls were learned behaviors or instinctual.
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29 .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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30 .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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31 .Now the sounds are too fast for us to be able to hear the differences.
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32 .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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33 .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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34 .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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35 .And this similarity helps parents recognize their nestlings after they\'ve left the nest.
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36 .(male student) Why do they need to recognize each other?
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37 .(female professor) Because parrotlets parents continue to feed their fledglings for about 3 weeks after they\'ve left the nest.
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38 .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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39 .(female student) So, but what exactly does this have to do with why parents in captivity mimic human voices?
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40 .(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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41 .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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42 .So, we have the first verified explanation for why mimicry is so important to psittacines in the wild.
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