Age- and sex-related variation in song-control regions in Cassin's finches, Carpodacus cassinii.

Male Cassin's finches (Carpodacus cassinii) sing long, complex songs that incorporate many elements mimicked from other species. Although one-year-old males (males in their first breeding season) are sexually competent and do breed, they sing a simpler song (fewer syllable types) than do males two or more years old (called after-second-year males). Females do occasionally sing, but with much less stereotypy and complexity than breeding males of any age.