2012年12月22日托福
TOPIC：鸟类叫声
讲鸟怎么学唱歌，三种方式：遗传；听自己唱然后不断纠正；听别个成年鸟唱然后学。证明遗传是说有些鸟把蛋下在别个窝里，然后幼鸟由别个养大但是一样能唱歌；证明学习时说聋鸟虽然也能唱但是不完整。最后说鸟的唱歌很精确到有很多dialect，然后鸟夫妻们利用这种dialect的区别来找到对方。最后一段是说他们之间相互模仿能够达到唱到一样的程度。
幼鸟学声
The songs of different species of birds vary and are generally typical of the species. In modern-day biology, bird song is typically analyzed using a sound spectrograph. Species vary greatly in the complexity of their songs and in the number of distinct kinds of song they sing (up to 3000 in the Brown Thrasher); individuals within some species vary in the same way. In a few species, such as lyrebirds and mockingbirds, songs imbed arbitrary elements learned in the individual's lifetime, a form of mimicry (though maybe better called "appropriation" [Ehrlich et al.], as the bird does not pass for another species). As early as 1773, it was established that birds learned calls, and cross-fostering experiments succeeded in making linnet Acanthis cannabina learn the song of a skylark, Alauda arvensis.⑴In many species, it appears that although the basic song is the same for all members of the species, young birds learn some details of their songs from their fathers, and these variations build up over generations to form dialects.⑵
Song learning in juvenile birds occurs in two stages: sensory learning, which involves the juvenile listening to the father or other conspecific bird and memorizing the spectral and temporal qualities of the song (song template), and sensorimotor learning, which involves the juvenile bird producing its own vocalizations and practicing its song until it accurately matches the memorized song template.⑶During the sensorimotor learning phase, song production begins with highly variable sub-vocalizations called "sub-song", which is akin to babbling in human infants. Soon after, the juvenile song shows certain recognizable characteristics of the imitated adult song, but still lacks the stereotypy of the crystallized song – this is called "plastic song".⑷Finally, after two or three months of song learning and rehearsal (depending on species), the juvenile produces a crystallized song, characterized by spectral and temporal stereotypy (very low variability in syllable production and syllable order).⑸Some birds, such as Zebra Finches, which are the most popular species for birdsong research, have overlapping sensory and sensorimotor learning stages.⑹
Research has indicated that birds' acquisition of song is a form of motor learning that involves regions of the basal ganglia. Further, the PDP has been considered homologous to a mammalian motor pathway originating in the cerebral cortex and descending through the brain stem, while the AFP has been considered homologous to the mammalian cortical pathway through the basal ganglia and thalamus.⑺Models of bird-song motor learning can be useful in developing models for how humans learn speech.⑻In some species such as Zebra Finches, learning of song is limited to the first year; they are termed "age-limited" or "close-ended" learners. Other species such as the canaries can develop new songs even as sexually mature adults; these are termed "open-ended" learners.⑼⑽
Researchers have hypothesized that learned songs allow the development of more complex songs through cultural interaction, thus allowing intraspecies dialects that help birds to identify kin and to adapt their songs to different acoustic environments.⑾
鸟类方言
The Dialects of Birds⑿
BIRDS sing in dialects as distinct to the avian ear as the difference between a Boston and Mississippi accent is to humans. But there has been a long debate over the significance, if any, of local differences in the songs of a particular species.
According to one major theory, birds are inclined to choose a mate with the same dialect because that helps keep the local group together, thus selectively preserving inborn behavior patterns and capabilities that are most succesful in coping with the local environment.
Scientists studying brown-headed cowbirds have developed a new theory. They believe the female bird cocks an educated ear to the accent of the male in choosing her mate, not so much from chauvinism as from the assurance that the right song means that the male is biologically fit.
The new idea is proposed in the ornithological journal Condor by Stephen I. Rothstein of the University of California at Santa Barbara and Robert C. Fleischer of the University of Hawaii. Their theory is based on observations of the brown-headed cowbird in the eastern Sierra Nevadas. Cowbirds are notorious among bird fanciers because they lay their eggs in the nests of other species, thus shirking the duties of parenthood.
The birds also have a considerable repertoire of sounds, including whistles in flight and elaborate songs used when they perch together. The female cowbirds respond respond more frequently to the local dialect than to males with a ''foreign'' accent.
The scientists said it seemed to be difficult for a cowbird to learn a new dialect. If that is the case, they argue, the female is assured by the local accent that the male is mature and has been around long enough to demonstrate an ability to defend its local territory - in short, a biologically fit mate.
Does this have any relevance to human accents? The researchers leave that conjecture to others.
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