Aru Bahl, age 11, of Benson, Ariz., for his question:

WHY DO BIRDS SING?

For countless ages, people assumed that birds sing love songs during the courting season, with perhaps a few joyful encores to welcome the spring. Then in 1920 that pleasant theory was questioned. On the basis of more accurate observations, we now know that most birds sing for far more practical reasons.

In our southern regions, the earliest bird songs already have begun. In a few weeks, as spring spreads throughout the land, their lilting tunes will be heard everywhere in woods and meadows, parks and gardens. This wondrous opera season, of course, corresponds with the nesting season.

Since the males are the songsters of the bird world, it is natural to assume that their lyrical arias are serenades to attract the females. In some cases this may be true. However, most male birds are devoted parents and their singing is a frantic effort to make sure their offspring get off to a healthy start in life.    

This, of course, calls for a plentiful supply of the right foods  within a fairly short shopping distance of the family nest. It seems these songsters have a strong inborn sense of territory and property rights. When they return in the spring, they need to stake out private claims to a suitable hunting area around their nests.

Each species warbles his own special tune as a no trespassing signal to certain other birds. For example, the robin's major problem is other robins who also hunt for worms, seeds and berries. So when he selects a mate and nesting site, he starts to sing with all his might. His throaty notes echo to the ends of his territory. Other robins are supposed to nest and hunt outside his range.

As a rule, the system works very well. After the nests are established, most parent birds hunt beyond earshot of their nearest relatives. In this way the hard working parents can count on enough suitable food for their hungry chicks.

However, sometimes the rules are broken and an aggressive male dares to invade the private property of a neighboring relative.  It is true that rival males often fight over females, though usually not to kill. But their fiercest fights occur over territory, and almost always the trespassing bird is ousted.