It's a noisy time of year in city and country where birds engage in audio combat with everything from other birds to heavy equipment, jet airplanes, lawn mowers, trucks on the highways and boom boxes. That such tiny creatures can make so much noise is one of the wonders of the outdoor world, but it's even more amazing what you can learn by listening to the avian symphony that's free for the hearing.

You've heard the concert since you were born, but do you really listen and understand what's going on out there in the trees, shrubs, and multi-flora roses? Here are a few bird song facts that every outdoorsman and woman should file away for future reference:

Only males sing, except...One of those biological facts of life that enrages rabid feminists who apparently wish things were different, but the facts are plain in this case of male-female role playing. With very few exceptions, only male birds deliver songs, and songs are usually heard mainly during the mating and nesting season. I understand that both sexes are songsters in species outside the Western Hemisphere. North American feminists can take comfort in the fact that only female birds lay eggs.

Songs and calls. There are two general categories of bird vocalizations--songs and calls. Songs are the longer, often complex, vocalizations you hear before and during the nesting season. Calls are heard all year long and usually have some communicative value to other birds. For example, if you have cardinals around your bird feeder, you'll hear both the male and the female making loud chirps while they feed. Those chirps are calls as opposed to the loud and varied songs which both the male and female cardinal sing.  Cardinals are an exception in North America because of this female song-singing ability.

Why birds sing. As a general rule, birds sing in connection with sexual reproduction. Biologists over the years have found that birds sing to stake out and defend territories, to identify themselves, to attract the opposite sex, to stimulate nest- building and mating, and to encourage the female to incubate her eggs. Some studies suggest that sometimes, male birds sing simply because they're happy or enjoy singing.

Imprinting young. There is strong evidence that baby birds hear their species' song while still inside their shell. The song is imprinted on their brain circuitry at this time. Young produced from eggs incubated in isolation from their species' song are unable sing the "right" song when they mature. They are able to produce a rudimentary song, but are unable to produce the species' adult song.

Cowbirds are a mystery in this regard, because they are "parasitic." Female cowbirds lay their eggs in other birds' nests and invest no time in rearing young; however young cowbirds grow up and make cowbird calls and songs, apparently without being imprinted with their own species' vocalizations.

Birds have accents. While it's easy enough to identify a cardinal song in Key West or in Indiana, there is marked variation in the details of those songs. Biologists call these differences "dialects," and dialects appear in birds that live as close as a few miles apart. As in human speech, however, the farther apart the birds, the more marked the dialect or accent. Nobody knows exactly why this is true, but it may have something to do with the process that eventually creates sub-species of the same bird as with the western thrashers or kingfishers around the world.

Songs and appearance. In some species, there is a direct relationship between the species' song and appearance. The best example is the Gray Catbird. Catbirds deliver a long series of song phrases stolen from other birds, mammals and machines as well as their own species-specific calls.

Theory is that catbirds do this to fool other birds into thinking their territory is densely populated and thereby deterring prospective competitors from moving into said territory. Note that catbirds are dark gray and very hard to see when in thick vegetation where they nest. This "cryptic" coloration helps them fool other birds who would know the catbird's false population message was a lie, if they were to spot the catbird singing it. Listen to a catbird singing sometime. It sounds like a whole lot of birds singing to me, a cacophony.

Songs and aggression. One of the most famous studies of bird song was conducted with white-throated sparrows. Biologists played a male white-throated recording near a live, singing male during nesting season. The male immediately flew to the record- er's speaker, perched atop it while singing and defecated on the speaker. Since injury usually means death to a wild bird, the value of song duels as an alternative to physical combat is obvious. It is rather whimsical too. There is plenty more than singing involved, especially if there is a family of Blue Jays in the area.

Songs and size. You may have noticed that often the smallest birds have the most interesting songs. The various wrens, for example, are among the smallest birds in North America, but they have incredibly loud voices and many complex songs. On the other hand, while bald eagles are among the largest of all birds, their "song" and calls are unremarkable unless threatened by some predator like a human. Eagles are loud, but they have a limited vocabulary.

While this phenomenon has not been explored, one obvious conclusion is that the eagle doesn't need to be a good public speaker when it can rip most avian competitors to shreds. On the other hand, the tiny wren's verbosity helps it survive in the habitats where they live and compensates for lack of brawn.

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