Froggie went a courtin'

On Sunday I stopped at Mill Pond Park to collect pond water for a program.  Around the edge of the pond I could hear a number of Green Frogs (Lithobates clamitans) calling loudly.  In time I located one nearby that let me approach within camera range.  The frog looks inflated like a ballon in this picture - its lungs are inflated with air.  To call this air is passed from the lungs to one or more flexible organs in its throat known as vocal sacs.

Green Frog - inflated with air and ready to call

When a Green Frog calls it produces a series of single notes that sound like someone plucking the same string of an out-of-tune guitar over and over again - "plunk plunk plunk".  In the photo below you can see that the frog has inflated his vocal sacs and is calling.  If you look closely, you can actually see the sound wave traveling across the surface of the water.  Look along the frog's side and in the dark water at the bottom right of the photo for a series of concentric lines traveling away from the frog. 

Calling Green Frog - note the sound waves on the water's surface

Nature is pretty awesome!