Nature’s finest song
The dawn chorus is a wonder of nature that is truly appreciated by the early risers among you – but how do birds sing and why do they do it?
The dawn chorus is one of nature’s greatest glories at this time of the year and we reveal how birds sing and why do they do it
BY THE TIME you’re reading this, the chances are you’re waking every morning to one of the great glories of the natural world in Britain – the dawn chorus. Seemingly every bird in the neighbourhood lifts its voice to herald the coming of daylight, building from a few hesitant notes from early risers like the Blackbird to a wonderful crescendo once everyone else joins in. This is nature’s alarm clock at its finest.
Now you don’t need to do anything other than appreciate its own beauty, but if you can start to unravel some of this glorious tapestry of song, and start to identify the individual strands, you’ll find your overall bird ID skills improving, too. Species that you hadn’t thought were present in your area will reveal their presence. Now is the time your #My200birdyear list will start to grow and grow. But why do birds sing, and how? The answers, as you might expect, are complicated…
Songs vs calls
Birds use their voices to communicate because it’s an efficient way of doing so, especially for smaller birds that live in habitat such as woodland (and remember that most of our garden birds are woodland or woodland edge specialists). Indeed, some of the smallest birds, such as the Wren, have the biggest voices, for just that reason. But not every sound that a bird makes from its beak is a song. There are calls, too – these are usually short, clear, loud and unambiguous, and each signals something different. It might be to maintain contact with other birds – listen to a skein of geese calling to each other as they fly – or it might be to alert others to danger, such as the unmistakable alarm call of the Blackbird. Song, though, is far more specialised, to proclaim a territory and to indicate to others that the singer is healthy and ready to breed. For that reason, of course, birdsong peaks during spring, when there’s little else on a bird’s mind.
Who sings?
It’s a strategy that’s most fully exploited by a group of birds called Passeriformes, literally, ‘perching birds’, which make up around 60%
of the world’s 10,000 or so species. And it’s usually the males that sing, although there are exceptions, such as Robins, where both sexes do so.
What does the song mean?
Firstly, it identifies the bird to others of its kind (and, of course, to you!). Secondly, it says something about the physical condition of the singer, so that any listening females can choose a mate in good condition, with the stamina to breed and then (in many cases) feed a family. To some extent, the male bird is saying ‘look at me! I’m so successful, I can afford to spend time and energy on singing this song, rather than foraging for more food’. Thirdly, it warns off other males who might be thinking of muscling in on our singer’s territory and/or mate, without them having to come to blows. Again, evolution has fastened on the most efficient way of perpetuating the species – actual physical battles could be disastrous for both of the birds involved.
When do birds sing?
For the most part, in the breeding season, roughly from the start of February to July, when they start moulting and have to think about staying hidden from predators. Again, there are exceptions – Robins sing throughout the winter, although that’s to defend feeding territories (hence why females sing, too), and Mistle Thrushes, too, are known for singing in midwinter (hence their old name of Stormcock). For most birds, though, the instinct to sing is triggered by an increased amount of daylight as winter starts to move into spring.
Robins sing throughout the winter, although that’s to defend feeding territories (hence why females sing, too), and Mistle Thrushes, too, are known for singing in midwinter
What is so special about dawn?
There are several reasons why so many birds sing at dawn. For a start, the male birds are announcing their survival of the night, no small feat when predators, weather, and the constant need to find enough food is considered. A male that has survived is not just available for breeding – he is telling any females listening that he’s easily able to supply himself (and potential mates and chicks) with enough food. Secondly, there’s a territorial function. Males are warding off other males, so that vital food supply is not overused. For other males, song helps delineate territories, and reveal any gaps where they could set up on their own. Thirdly, many female birds lay eggs at first light, and are at their most fertile immediately afterwards, so singing serves to ward off other males who might be thinking of attempting to mate with them. There could be other benefits, too. Dawn is generally quiet and still, so sound carries further (this is also the reason suggested for urban Robins singing at night), while some species are unable to feed at dawn and so might as well spend the time doing something else. Taking this last point, there’s certainly a logical progression in the way the dawn chorus develops – birds that feed on flying insects, for example, have to wait until the day has warmed up a little and their prey has become active, while those that eat worms can start earlier. So, Robins and Blackbirds sing early, and get the worm, as the old proverb suggests, while warblers generally join the chorus later. Finally, there’s also a dusk chorus. It’s not quite as all-inclusive or as loud as at dawn, but many species do join in, and for many of the same reasons as at the start of the day.
How do birds sing?
OK, here’s the science bit. Basically, a bird takes in air through its bill, on into its windpipe (or trachea). This then forks off to each lung, and after the air is processed there, it is exhaled by the same passage. This system has the secondary purpose of producing sounds. The bird has a ‘voice box’, called the syrinx, at the point where the windpipe divides. This is effectively double-barrelled, and allows birds to produce two different sounds simultaneously, obviously of great advantage in building a complex song. Each half of the syrinx consists of a pair of organs opposite each other on the wall of its bronchus – a little tympanum, or elastic membrane, which is effectively a vocal chord, and a small lump of tissue. The bird forces air past these two organs. The diameter of the tympanum can be varied, and the degree to which it protrudes into the bronchial tube, and sound is created by the passing air vibrating the tympanum. Its pitch and loudness can be varied by the size and position of the tympanum, and the lump of tissue (which is extendable) is thought to help change loudness without changing pitch. Given that each half of the syrinx can work independently of the other, you can imagine how some songbirds can produce music of extraordinary complexity. For those birds which sing particularly long songs, too, the ability to sing while inhaling is obviously a necessity. The end result is an array of sounds more complex than any others in the natural world. Functional, practical, vital for life, yet beautiful, too – no wonder birdsong has always inspired human musicians, poets and other writers. Just as when you’re learning a foreign language, for humans, learning birdsong is best done stage by stage, starting with the simplest and/or most commonly heard songs. Taking your time and hearing the same song over and over again is the key – you’ll be surprised how easily you ‘get your ear in’. Once you’ve mastered some of the basics, you’ll find that unusual songs stand out, even in a dawn chorus or a noisy spring woodland. Here’s our quick guide to learning 10 bird songs. Remember that similar songs don’t always come from similar species, so be prepared to think laterally. Get to grips with these, and you should soon be able to identify 20 more…