We call it birdsong, but how much of it is song in the sense that humans employ? How much of it is declaration of territorial rights, and not necessarily melodious. Or a sort of early morning bugle-call to announce another day? (The dawn chorus.) And warning cries at the approach of a hostile being: a cat, say, or a feathered predator. The dawn chorus may be easing off now, with birds well into the rearing of their young. But still, in the early hours there are stirrings and soundings-off - and pure melody to be heard. A friend used to creep out with his recorder early on spring and early summer mornings to listen to a thrush, whose ringing notes seemed, in addition to being a greeting to the new day, also to contain a lovely melodious theme, along with a running up and down the scale.
This friend convinced himself that he could whistle a few bars in imitation of the thrush, and the bird, after a pause would send the same notes back to him. He says he has a few recordings to prove this. Lewis Thomas in The Lives of a Cell, has it that the robin "sings flexible songs, containing a variety of motifs that he arranges to his liking". The same writer attributes to the nightingale 24 basic songs, but the bird varies the arrangement of phrases and the length of pauses. Gilbert White in his Natural History of Selborne notes the changing calls of birds according to the seasons. Some utter notes all the year round for the purpose of keeping together, but many have cries "peculiar to the love season," which are uttered to summon the mate or as a cry of distress when the breeding grounds are invaded.
He then lists "singing birds, strictly so called" which continue in full song till after Midsummer. They include song-thrush, wren, redbreast, hedge-sparrow, blackbird, goldfinch, among those who cease full song before that date, including chaffinch and nightingale. He makes a point of using the word sing.
The poets are in no doubt, as with Ferguson's elation "as I hear the sweet lark sing,/In the clear air of the day." While Shelley's skylark is addressed: "And singing still dost soar, and soaring ever singest."