Recordings of bird calls are available at eNature.com, The Cornell Lab of Ornithology Macaulay Library and Naturesongs.com. The eNature.com archive covers over 550 species in North America, while Macaulay Library claims to have recordings of 75 percent of all bird species worldwide.
ENature is a website focused on the fauna of the United States. Its selection of bird calls is available for free and is organized by broad groups, such as gull-like birds and sandpiper-like birds,rather than by taxonomy.
The Cornell Lab of Ornithology Macaulay Library bills itself as the largest archive of animal sounds in the world. Although visitors can listen online, they cannot download audio. To acquire copies of audio, individuals must order tracks. Bird calls are available via a search engine the site provides or by browsing a taxonomic listing.
Naturesongs.com offers a diverse range of bird sounds for non-commercial use with permission from the original recorder. Unlike the other two websites, the audio on Naturesongs is all the work of a single author, naturalist Doug Von Gausig. Audio is organized by taxonomic group.