Song development in the indigo bunting

Abstract

Five male indigo buntings, from 3 to 7 days of age, were hand-reared in isolation from adult indigo buntings. As soon as the young birds began to sing subsong, between 15 and 60 days of age, they were isolated from all other indigo buntings until their songs were fully developed. Early subsong was a variable warbling. During the first spring this ‘crystallized’ into a series of figures which eventually formed the entire song of the bird. In the fully developed song the figures have a regular shape and may be repeated. The songs of the isolated birds contained very few figures which were closely comparable to those of wild birds recorded in the area of the nests in which they hatched. Sibling nestlings developed completely different songs. This suggests that learning of the song does not take place before the young leave the nest. The songs of the isolates are longer than those of wild birds, have about the same number of figures per song, but fewer kinds of figures per song, and a longer interval between songs. The frequency envelope is narrower and lower. The general characteristics of figure shape, spacing and repetition of figures, frequency range, and even the interval between songs, however, are all close to those of free-living birds. The detailed characteristics of the wild indigo bunting song seem to be learned, but this learning seems to involve primarily a refinement of a basic pattern which the bird is able to produce without ever having heard an indigo bunting song. Birds which were ‘tutored’ by playing songs of wild birds added new figures to their songs up to 18 months of age, past the spring crystallization of their songs in isolation.