One of the earliest sounds of spring at the refuge comes from the spring peeper. These nocturnal tree frogs do not generally get going until the sun begins to drop. Then they set off a great chiming sound that is all-enveloping. The singers are males announcing themselves to prospective mates by inflating and deflating a balloon-like vocal sac on their necks. Tree frogs are hard to spot as they are tiny -- just 3/4 to 1 1/2 inches long.

Above: A male spring peeper calling (video).