How Birds Develop Song Dialects

Abstract

Individual songbirds frequently share, in varying degrees, their repertoires with others on neighboring territories. At the same time, repertories differ between localities, giving expression to the term "dialect". How dialects form, illustrating 1st with the cardinal and then considering other species, especially fringillids is considered. Conformity is seen principally as the result of copying by young, a process which is limited in most species to a period from the time when the young leave the nest until the motor patterns develop the following spring. Reared without experience of song, birds develop some features such as general structures of syllables and repetitions of syllables and songs. These facts suggest inherited motor and sensory influences. Individuality of songs is determined by a variety of influences, the major ones being: the interactions of the time-limited copying process with dispersal of the young arising from the area of rearing to their new place, the active modification of syllables through drift, and the reordering of syllables within songs. These individual characters are in turn copied by young males. In this way local peculiarities are built up within a population. The integrity of a local dialect is maintained in cardinals by a high return of adults to their territories from year to year and low annual mortality. Also, young often disperse to relatively short distances from home nests. However, many individuals disperse over considerable distances and probably introduce novel patterns to certain localities. Such dispersal also probably has the countering effect of making some patterns widespread over fairly large areas as in Ontario [Canada]. In other species conformity varies from high to low, although in all groups there is evidence of copying and improvisation. The differences depend to a great extent on which tendencies dominate. A model of development based on calls, copying, improvisation and reordering of syllables is presented. This model is seen to apply to oscines in general. Problems associated with the development of song are discussed, particularly those based on the concept of innateness.