Song behavior refers to complex vocalizations used in the context of mate attraction and territorial defense. Birds that produce such sounds are commonly called songbirds. Technically songbirds constitute species in the avian order Passeriformes. This is by far the largest avian order and contains about half of the more than 9,000 living bird species. The songbird order, one of the most recently evolved, includes familiar avian groups such as sparrows, swallows, starlings, canaries, finches, warblers, jays, titmice, crows, wrens, robins, and buntings. This order can be further divided into two suborders, the Oscines (members of the suborder Passeres) and the sub-Oscines (a much smaller group that includes the flycatchers of North America), which appeared earlier in evolutionary history and is thought to be more primitive. All songbirds produce complex vocalizations, but there do appear to be qualitative differences between Oscine species and sub-Oscine species in vocal development...