No, that lovely sound you hear in the evening from your Rincon Vacation Villa is not a bird but a frog! It is the El Coqui frog, mostly heard after a little rain.
From Welcome to PR: "The coquí has been a cultural symbol of Puerto Rican history for centuries. Since the time of our native Taino inhabitants and its presence shown on many stone engravings to the present and all the places and objects you will find this symbol represented. It has become a national symbol and an icon for anything Puerto Rican. When Puerto Ricans want to express their nationality, they say: "Soy de aquí como el coquí" (I'm as Puerto Rican as a coquí)"