Frogpocalypse

I live on a lake and this is what my back patio sounds like every night. They live in the branches of the weeping willow trees that dip down to the water. The sound starts with one frog, then a few join in, and soon there as a chorus of them on all ends of the lake in all tempos going at once. Then when a crescendo is reached, they all start to stop one by one until it's silent again. But the silence only lasts for minute, and then the cycle repeats. I don't know if it's some huge frog mating ritual, or family reunion.