Why do Tree Frogs Sing?

From :www.america-alfresco.com

Tree frogs communicate by singing to each other during the early part of summer evenings. On many nights I've kept my window open so I could fall asleep while listening to the sounds tree frogs, crickets and spring peepers.

Tree frogs sing until about two or three o'clock in the morning and stop well before dawn. In addition to darkness, I suspect that humidity plays a role in the tree frogs' singing habits.

Tree frogs break out in song on hot, humid summer afternoons just preceding thunderstorms.When you hear the frogs sing during the day, you know there's a good chance a storm is not far away. In a way, tree frogs act as nature's barometer.