I finally located a European Starling in a tree next to my window mimicking the whole series of songs again. It reminded me of David Attenborough's TV special The Life of Birds. The following is a clip from the special showing the Lyrebird trying to attract a mate. The Superb Lyrebird is thought to have the loudest bird call in the world.
So how do birds produce such a complex variety of notes?
Birds have a syrinx, a sound-producing organ, that is the equivalent of the human sound box. But it is situated much lower down, at the junction of the two bronchi or air tubes leading to the lungs.
This means that the syrinx has two potential sound sources, one in each bronchus. The separate membranes on each bronchus produce separate sounds, which are then mixed to produce a far greater variety of sounds than humans.
The best time to hear bird song is at dawn. One reason may be that dawn is the best time for sound to travel. Or it may be because it’s still too dark to do any successful foraging.
Bird song has two main functions: to defend a territory and to attract a mate. Male birds generally use shorter, simpler songs for territorial defense. Gaps in the song enable the singer to listen for replies, and determine where their rival is and how far off.
When they are trying to attract females onto their territory, males sing longer and more complex songs.
If you're not sure which bird sings what song the book Bird Songs: 250 North American Birds in Song is very popular. It's a beautiful coffee table book that allows you to enjoy bird songs at the touch of a button and a joy to children just learning about birds.