Never heard of them? Neither had I, however we have all heard them and mistaken them for frogs or just assumed we were hearing general marsh sounds. This is one of the many songs they sing:
The Sora is found in freshwater marshes, flood fields, and swamps, where they walk around like little chickens pecking at the water. The biggest threat to these birds is wetlands being drained, as this is where they nest. Having been over hunted, they have made a come back due to the high survival rate of chicks.