The importance of development: what songbirds can teach us.

Birdsong is a sexually selected signal that is learned early in life. Song learning (imitative vocal learning) by male songbirds has been extensively studied, but other aspects of development are important in birdsong as well. Female experience with song can affect song preferences in some species but not in others. The neural responses to song in females, as assessed by immediate-early gene expression, likewise appear related to early learning in some studies but not others. The development of song preferences by females requires further study to determine how genes interact through experience to produce adult preferences. Male song learning appears to be affected by exposure to environmental stressors during development. Developmental stressors impair both neural development and song learning. Thusly female song preferences may guide females to mate with males who have had benign developmental conditions and/or high developmental stability. These lines of research highlight the importance of considering development whether examining the function or the mechanisms of behaviour.