The Origins of Music: Preface - Preface

Nisdorf-Bergweiler,and DeVoogd 1995).Both studies uncovered few

differences in the brains of control and experimental groups,indicating

that most neural changes are likely to be developmental rather than a

cause or consequence of song learning.However,one effect that did

persist between tutored and untutored zebra finches was the number

of dendritic spines in a region of the anterior forebrain loop (LMAN;

Wallhauser-Franke, Nisdorf-Bergweiler, and DeVoogd 1995). The

number of dendritic spines was significantly smaller in birds that had

learned to sing,supporting the idea proposed by Changeux and Danchin

(1976) that learning may involve pruning unused connections between

neurons.

Innate Preferences Guide Song Learning

The second learning constraint is the predisposition to learn songs of

one’s own species (Thorpe 1958;Marler 1970;Marler and Peters 1977).

With the exception of mimics such as starlings and mockingbirds (Mimus

polyglottos),most birds,when given a choice,prefer to learn the songs

of their own species.Vocal learning was studied in the laboratory with

sparrows collected as nestlings before they had an opportunity to learn

songs.The birds learned readily from taperecordings during the sensitive

period that extends from one to four months of age.Work with sparrows

and other species uncovered an interesting paradox:young birds must

hear the songs of their own species in order to learn them,but when

faced with a potentially confusing array of songs,they are able to select

the ones of their own species to serve as learning templates.

Young birds raised by their parents in the wild presumably hear a

range of sounds,including songs of other species that inhabit the same

geographic range.One might assume that they decide which sounds to

memorize by observing their parents (most likely their fathers) singing.

However,laboratory experiments with tutor tapes in which social cues

are not available produce the same outcome.Another possibility is that

the size and structure of the vocal tract limits the type of sounds that can

be produced,predisposing the bird to learn the correct song.Clearly

some anatomical restrictions come into play in the sense that it would

be impossible for a hummingbird to produce the call of a crow.However,

birds can be induced to learn the songs of other species if they are pre-

vented from hearing the ones of their own,establishing that anatomy

of the vocal tract does not dictate learning preferences (Marler 1991).In

conclusion,laboratory studies that remove social cues and provide learn-

able songs,including those of other species,reveal a learning bias that is

guided by instinct.

69 The Neural Basis of Song Learning in Birds

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