Douglas Von Gausig, University of Michigan Museum : ADW is an online database of animal natural history, distribution, classification, and conservation biology at the University of Michigan
Petr Myska: The VN database offers you an insight to the immense biodiversity of Mexico.
The birdsongs are available online in different formats. In order to listen to them, you will need the appropriate software and browser plug-ins. I recommend Winamp Media Player and the VLC Media Player, both of which can be downloaded for free.