iBird Explorer Pro is one of the best bird identification apps for smartphones I’ve found. It’s also available for Android smartphones.
Right now it’s on sale at the iTunes app store.
What I really like about this app is that you don’t have to guess, or know in advance which group a species you’re trying to identify belongs, unlike most birding books.
iBird Explorer Pro leads you step by step toward your identification. You enter information from your observation of the bird, such as: location, shape, size, habitat, primary color, observed month, wing shape, tail shape, leg color, crown color, nape color, eye color, bill shape, bill length, etc. and the app will then list the potential birds yours might be, and will display facts and photos about them, and even play a recording of their song.
The app really helps you identify the birds you’re photographing.