Diane Reehle, age 12, of Allentown, Pa., for her question:

WHY DO BIRDS MIGRATE?

Come fall we watch the birds gather and flock south for the winter. And every year, dozens of young nature lovers wonder why. Let's suppose that they stayed with us through the worst of the wintry weather. Many of them feed on insects, others on plant food. When the snow blows, the bugs and thriving green plants disappear. There is not enough food for all the birds who were here during the summer.

Migrating birds fly to mild‑winter climates, where their favorite foods are more plentiful. However, they, are crowded and there is not enough food to feed new families of growing chicks. So come spring, the parent birds fly back and spread far and wide. The air teems with insects, and the woods are popping with new greenery. As far as we know, birds do not mind the winter cold very much. It seems that the main reason for their seasonal migrations is simply a matter of groceries.