Birdsong

My monthly 'Nature Notes' column . . .

You’ve only to step outside our backdoor at the moment to be assailed by birdsong - though perhaps that’s the wrong word, as of course it’s a lovely sound. Bird vocalisation is a vast scientific subject, with lots of research going on as to how bird songs and calls develop, how they are used, and so forth. Almost all species of birds produce some sort of vocal sound, but it is the Passeriformes (the perching birds) that are particularly noted for their singing ability - birdsong being, I suppose, those bird calls that are tuneful to our ears.

In fact, bird songs can be quite complex;  by definition ‘song’ is more than a mere cheep or squawk, something relatively long and often melodious, and usually though not always associated with some aspect of courtship. Exceptions to this, such as the winter song of the robin, are linked to the need to establish and defend a territory. Interestingly, birdsong outside of the tropics is mostly delivered by the male, while many tropical species have song delivery shared equally by both sexes.  The vocal organ of birds is the syrinx, and songbirds have a number of muscles controlling this area of membranes over which air is passed, allowing a wide range of different notes and sounds to be produced, often at quite high volumes.

Why do birds sing?  As already stated, bird song is mostly related to reproductive activity. Songs are sung to attract a mate, and to establish and maintain a breeding territory. Often the male will establish a breeding territory and then seek to attract a mate to it, and the males of some migratory species will arrive before the females.

Song helps to stimulate and synchronize courtship, and indicates a readiness to breed.  This may be why both sexes sing in many tropical species, where breeding can happen at any time of the year and is dependant on food supply rather than season. The song can help to maintain the pair bond, and often fairly plainly plumaged birds, where male and female are not very distinct from each other, can have quite complex songs - with regional variations and ‘accents’.

There is certainly a competitive element to birdsong, especially where the more complex songs are involved. Males signal their effectiveness as mates by singing long and complex songs, to which they may well add new elements, perhaps copied from other sounds round about.  At this time of the year, many birds will sing from prominent positions - this is especially true of blackbirds, thrushes and robins; their songs may be used to intimidate opponents as well as to attract a mate.

Not all birds can easily be seen as they sing, however, so it’s good that songs are distinct - the RSPB and other organisations produce DVD’s of birds with the song for each species, a good way of learning to tell one from another. Anyway, there are some beautiful sounds to be heard at this time of the year - make the most of them!