Bird Vocs is an app to practice bird vocalizations. It connects to xeno-canto.org, and lets you use recordings from that website on your mobile device. Bird Vocs also draws the spectrograms (if available), and gives you the capability to compare two spectrograms overlayed or next to each other.
Please note, Bird Vocs will not automatically identify sounds for you. All recordings come from xeno-canto.org and are already identified.