Vocal learning

There are about 4000 species of song birds (Order Passeriformes, suborder Passeres).   In all species studied to date, vocal development is strongly influenced by auditory experience.  Modern experimental studies of song learning in birds began in the 1950's in laboratory of W.H. Thorpe.  He and his student Peter Marler used birds hand-reared from an early age to show that young male song birds learn their songs.   If a bird is reared without hearing the normal adult song of its species, a simplified "isolate" song is produced.

Here is the song developed by a male white-crowned sparrow raised in the laboratory from the age of 5 days without hearing the song of an adult.  Click on the spectrogram to hear the sound.  Compare it to the song developed by the next bird who was tutored with a tape-recorded tutor (the bottom song).

Here is the song developed by a male white-crowned sparrow that was tutored early in the first 2 months of life with a white-crowned sparrow song.

Here is the tape-recorded song he was tutored with.  Notice there are small differences between the tutor and the imitation, but overall the copy is quite good.   These small learning errors or improvisations introduce individual variation into the local populations of songs.