Songs are often used to claim territory or to attract mates.  Shorter calls are used to warn of danger, keep flocks together, announce locations of foods and for many purposes we don't fully understand.

The reason we call our hobby "birding" and not "birdwatching" is that birders often identify many birds by their calls and songs. In fact, calls often lead birders to a bird. That's because we can hear in all directions, but can only see straight ahead.

Learning calls is not hard. You probably already know the call of Canada Goose (Honk),a Mallard (Quack) or a Chickadee (Chick a dee dee dee).

A good set of tapes or CD's to learn from are the "Birding by Ear" ones by Walton & Lawson in the Peterson series. "Larkwire" is an app for a smartphone that teaches calls as well. But you can also learn calls by carefully listening to a bird while you're watching it through your binoculars.

Here are some links to help you hear some bird calls on the web: