Vocalizations

Northern Mockingbird

You have bird songs and calls. Songs are reproductive vocalizations. Everything else is a call. Songs are usually seasonal. Calls are usually single or double notes. Songs are hormone controlled and manipulated, whereas the timing and pattern of calls are not. Calls usually serve an alarm or aggresssive function. Calls also contribute to social organization and are used in echolocation Songs attract mates and are rigidly controlled. Songs are usually more complex than calls and the delivery pattern usually quite fixed.

Vocalizations can be drawn out in a sonagram, which is a graph with sound frequency on the y axis and time on the x axis.

In general, Passeriformes are the best and most complex singers. The Northern Mockingbird is famous for its mimicking ability. I've even heard one mimic a train. On the other hand, storks don't call (they have no syrnx), but clap their bills instead. Generally, the duller the plumage, the more likely a bird is a good singer, since color functions much like song.