Sunday, 29 November 2009
This so called 'sub-song' is a quieter and incomplete winter version of the full monty and is a well documented feature of some songbirds and blackbirds in particular. It is commonly attributed to young male birds practicing for the real deal to come in their first Spring. I rather prefer the anthropomorphic notion that it might just be adult males twittering on for the fun of it. After all, male Homo sapiens do this all the time. As you'll have noticed, there's always a phantom whistler tootling away somewhere.
Night singing has some other intriguing aspects. For example, people at Sheffield University did some research that seemed to suggest that robins sing more at night in cities than in rural areas so they don't have to compete with daytime traffic noise. (You can read more details about this here ).
Night singing does makes some kind of intuitive sense. For blackbirds, for example, the main purpose of the song is to attract and keep a mate (rather than territorial defence). So, why not take advantage of the quiet hours and sing a bit? Your voice travels further so you can conserve energy as you don't have to belt your song out so loudly to be heard by potential mates.
You would think that an additional contributing factor in trying to explain urban night singing must be street lighting. I don't know what its like where you are but our local council has been replacing the city's old sodium lights with new ones that are astonishingly bright and give a whiter light more closely matched to daylight. Its like dawn all night long and this must have some effect on the species that respond to daylight in the dawn chorus. The Sheffield researchers, however, say that the effect of light pollution, to which nocturnal singing in urban birds is frequently attributed, is much weaker than that of daytime noise.
On the other hand, maybe my blackbird singing in the dead of night was only waiting for the moment to arise...