Problem :

What are the three stages of bird song development?

Young birds first have a subsong, which is very unstructered. They then develop a plastic song, which contains structured elements but is still greatly variable. Finally they develop a highly structured adult song.

Problem :

What distinguishes the development of bird calls from songs?

Bird calls are mostly experience independent rather than learned. Bird songs rely heavily on learning from adult birds during development.

Problem :

How are the learning of songs in birds and languages in humans similar?

Both have a critical period in development during which an individual is most able to learn them.

Problem :

What are some general uses for learned song in animals?

Many species use song in mating rituals. Variation in song allows for competition between individuals. Song is also used by some species to identify individuals who are foreign to the area (and thus will have a different dialect of song).