It's not only the birds that are possessed of silky voices and interesting vocalizations, you know.
Anyone who is spending much time outside these warming days will have noticed other sounds - sounds from the amphibian world. If you are interested in learning about bird calls, you'll want to know about the above critter. It's a Spring Peeper, Pseudacris crucifer. These are tiny tree frogs, distinguished by that (more or less) X marks the spot on the back.
Enjoy the amphibious symphony will you can. It doesn't last long.