The Macaulay Library at the Cornell Lab of Ornithology has released online nearly 150,000 digital recordings of 9,000 animal species. The audio collection is the world's oldest and largest library of sounds, and curators said they are working on improving search functions and collaboration tools to expand access to a larger public. "It's just plain fun to listen to these sounds," said one curator. "Have you heard the sound of a walrus underwater? It's an amazing sound."