Susan Warick, age 12, of Costa Mesa, California, for her question:

What do songbirds sing?

No, they don't sing to entertain us, though Andy has a mockingbird friend who answers back. He seems to enjoy copying a tuneful phrase and even makes smacking sounds that could be returned kisses. But whatever his musical motives are, they do not agree with what most experts think about other songbirds. As a rule, the singing is done by the male bird. Then perhaps he is serenading his lady love. This, say the experts, is not so either.

It seems that all the lyrical warbling is a threat to warn other birds from the nesting site. This is logical because the growing family needs lots of food within shopping distance of the nest. The most worrisome neighbors would be close relatives, who dine on the same foods. Each species has its own repertoire and a songbird sings mainly to trespassing cousins. He means, Go Find Yourself a Home Somewhere Else. Though he says it very prettily, if his warning is not heeded, he is ready to fight fiercely for his territory.