Delayed vocal ontogeny in songbirds: a laboratory study validates a model for delayed development derived from field studies

Abstract

Based on field studies, we proposed a model that describes how vocal ontogeny proceeds over a 2-year period in wild brown-headed cowbirds (Molothrus ater). We tested this model in the laboratory by exposing yearling male cowbirds (n = 7 tutees), trapped at the start of the breeding season in a southern California dialect, to adult tutors with unfamiliar song types from a different dialect. As adults at the start of their second season, the tutees all had enlarged repertoires based almost entirely on tutor song types. Thus, tutees dropped song types in their yearling repertoires that did not match tutor types and added tutor songs that they had heard for the first time as yearlings in captivity. We discuss these findings in the context of a previous captivity study in which tutees also changed their yearling repertoires but generally failed to copy their tutors’ songs. This is the first laboratory study to fully replicate the delayed ontogeny we have described for wild cowbirds, and validates the delayed vocal development model we proposed. This model is important in a more general context, because it explains how song dialects can remain temporally stable despite immigration by young males with non-local songs.