Bird Vocalization - Learning

Learning

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", 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. In 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.

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. During 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". Finally, 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). Some birds, such as Zebra Finches, which are the most popular species for birdsong research, have overlapping sensory and sensorimotor learning stages.

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. Models of bird-song motor learning can be useful in developing models for how humans learn speech. In 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.

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.