Environmental factors affecting song control and song perception in songbirds

Abstract

In songbirds, the differentiation of song and the song control system in the brain is mediated by the action of gonadal steroid hormones that are influenced by environmental factors such as day length, food availability, and social relationships. In particular, the Canary (Serinus canaria) and the Zebra Finch (Taeniopygia guttata) have become widely used animal models to study these brain and behaviour relationships. The evolution of complex male songs is thought to have evolved through sexual selection. For example, male Canaries produce elaborate songs some of which contain syllables with a more complex structure (sexy syllables) that induce females to perform copulation solicitation display as an invitation to mate. Females also show a differential expression pattern of immediate early genes and androgen receptors in the auditory forebrain in response to male song quality. In male songbirds, the amount of learned motor patterns is not always linked to the size of brain structures involved because the overt song memory may differ from the total memory of individual birds, for example when they use distinct sub-repertoires in different seasons. Further, male birds that have been raised under a restricted acoustic and social environment show a different modulation in song repertoire and brain differentiation that can be changed in later life when brought into a new social context. Similarly, developmental stress can also have an impact on song and brain development. Thus, the characterisation of song memory formation and permanent song motor memories will help to understand the neural mechanisms of song learning.