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In the mornings, youre hearing the first, tentative music of songbirds, as they tone up their lungs for the annual mating season. Birds sing primarily to attract mates and establish nesting territories. But behind that simple sentence, many surprising stories lie.
To begin with, most songbirds arent born with their songs intact. They learn to sing the way human beings learn so speak -- by listening to their parents. At first, their songs are a sort of babble, like baby talk. With practice, they put the notes and cadences together.
If a hatchling is raised by a bird of another species, it will learn the wrong song, which puts it out of the mating game.
Its different with most mammals, whose sounds are hard-wired into their genes. A dog will bark and a mouse will squeak, no matter who raises it. Some birds are hard-wired, too. Doves will always coo and owls will screech. Only songbirds especially those classed as Passeriformes -- or perching birds-- have options. There are often local accents. Black-capped chickadees sing slightly differently, depending on where they live.
Among songbirds, males do most of the singing engaging in long and complex song duels to prove themselves. The length and tone of the males songs are clues to their virility. Robust singing indicates a healthier bird or one that controls a more productive feeding territory. That makes it more likely that hell be able to provide food and defend a female when she is sitting on the eggs. The female listens carefully to whats on offer. After several days of listening, she will select a mate.
Male combat songs demonstrate their ferocity without having to risk injury through actual combat. They give other birds specific information about the location and identity of the songster. The male will evaluate any replies, to determine who the rival is and how far he is away. The bird can tell the songs of males parked legitimately in neighboring territories from those of a new and potentially threatening interloper.
Song solves another problem birds face: the need to communicate with others of their species across considerable distances, while remaining concealed from predators. Sound travels in all directions. It can penetrate through or around objects without necessarily divulging the singers exact location, as many a birdwatcher will frustratingly attest.
In forests, where sound bounces off trees and is absorbed by the leaves, birds like the ovenbird use a rapid but penetrating song to ensure that their messages gets across. Out on fields and open spaces, birds like the savannah sparrow make a persistent buzzing sound which carries over long distances. Yet other birds, like yellow warblers, simply pick a tall cedar or other high perch and blast their message for all to hear.
Besides songs, birds have calls. A call is normally simple and short. Northern cardinals, for example, use a loud metallic-like chip. It warns other birds of danger or orders them out of the owners territory. Both males and females call.
Human activity is altering bird song. Birds have to be heard over everything from car engines in cities to oil and gas drilling in the desert and plains. Some birds simply leave the area when development arrives. Others stay but change the key they sing in, so they can be heard over the din. We do not yet have enough data to know what impact this will have on mating, if any.
Anyone who has tried to sleep late on a spring morning knows that birds sing the most and the loudest just around dawn. Scientists suggest several possible reasons for this. It could be that the dawn hours are the best time for sound to travel, as there is usually little wind and the least number of other noises about. Dawn is also a time when birds can do little else: the light and temperatures are low, insects are not very active and its hard for birds to see their prey. Another theory is that birds calorie reserves are low after the long night. By singing a robust song to a female, the male is advertising that hes still strong.
If you love bird song, the coming weeks are the time to throw open your windows and listen to the mounting chorus. By July the nesting season starts to wind down. The birds go into their annual feather molta vulnerable period. They become very quiet so that predators will not detect them..
Bird song is a highly complex topic that we are only just beginning to understand. But listen this spring, as the annual mating dance tunes up. Those birds arent singing for fun, theyre singing for their lives.
John Hannan is director of development for Audubon Connecticut and can be reached at jhannan@audubon.org.
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