From the Cornell Lab of Ornithology website:
For more than 80 years we have prided ourselves on maintaining and distributing recordings of the highest quality. Our collection of natural sounds includes more than 160,000 recordings, comprising 67 percent of the world’s birds, and rapidly increasing holdings of insects, fish, frogs, and mammals. The video collection includes more than 3,000 species and we are rapidly increasing the breadth of our holdings by adding assets filmed in high definition.
Recordings play a key role in learning animal identification as well as for survey work using playback protocols. Our engineers turn raw field recordings into high-quality sounds for our audio field guides. We often engineer sounds for conservation and commercial projects based on regional specifications. In addition to expertise in selecting, engineering, and mastering these recordings, we have significant experience in the technical process involved in making animal vocalizations sound as pure as possible, whether they are on a microchip or a surround sound system.
More here.