From the site’s intro:
xeno-canto is a website dedicated to sharing bird sounds from all over the world. Whether you are a research scientist, a birder, or simply curious about a sound that you heard out your kitchen window, we invite you to listen, download, and explore the bird sound recordings in the collection.
But xeno-canto is more than just a collection of recordings. It is also a collaborative project. We invite you to share your own bird recordings, help identify mystery recordings, or share your expertise in the forums. Welcome!
It truly is a remarkable collection of bird sounds, often cc-non-commercial licensed.