Bird chorus rife with meaning

The silence of winter is being supplanted by the exuberant springtime sounds of birds. Soon the full, noisy symphony called the dawn chorus will begin: Birds will wake up singing with the sunrise and their combined songs will build to a crescendo for several hours as the day advances. By mid-May, when most migrant birds have returned, this joyous chorus can jolt even the soundest sleepers awake.

As beautiful as birds can sound to our ears, they don't sing to sweeten our springs. They're communicating with each other, signaling the male's desire to leave his mark on the gene pool.

Robins, orioles, sparrows and cardinals are creating audio billboards designed to draw in a mate and ward off other males. Females listen closely, using a male's songs to gauge his fitness as a potential mate and ability to hold onto a breeding territory. (In a few species, such as cardinals and rose-breasted grosbeaks, females also sing.)

Song is an essential feature for birds, and its relative loudness is fairly unique in the animal kingdom, where most creatures prefer to remain as inconspicuous as possible. For birds, the danger presented by coming to a predator's attention is offset by a strong singer's success in breeding.

Practice makes perfect

We used to think that all birds hatched with their songs already stored in their brains.

Some species (such as phoebes, loons, ducks, owls and woodpeckers) do hatch knowing their species' songs. And there are a few accomplished mimic birds, such as the European starling and mockingbird, that pick up new sounds throughout their lives, but they're the exception.

A young male songbird listens closely to adult males to get a mental template of his species' songs. He'll spend his first summer and fall practicing, continually comparing and adjusting his own sounds to fit that framework.

Those practice sessions can be jarring, as young birds in midsummer shriek out song fragments before arriving at a passable song. But after months of running through a play list, the young males are ready to join the mating sweepstakes the next spring.

Many songbirds vary their songs to fit the circumstances, choosing from a repertoire of sounds if a female fails to show interest or another male encroaches. Research indicates that female birds prefer males with the most complex songs, perhaps because they sense that the best songsters have the largest brains.

There also is evidence that birds can adapt their songs to fit their circumstances. Researchers in Europe recently discovered that birds in cities sing shorter, faster songs at a higher pitch than their forest-dwelling cousins so that their songs can be heard over the cacophony of urban life.

If you're annoyed by a robin or cardinal singing loudly early some spring morning, remember that it's only a temporary annoyance. As soon the bird finds a mate and begins to build a nest, he'll be too busy to sing.