We can see birds with our ears. Through trees. Around corners. In the dark. An Eastern Phoebe singing out fee-bee from the top of a tree overhead.
Birding By Ear CD teaches how to know birds by their sounds.
This invaluable aid seems to be going away. The publisher plans not to re-issue it after it sells out. Already the Backyard version and the Western version are unavailable.
The Eastern North America version is still available, but we don't know for how much longer.
This is how I learned to watch birds with my ears. If you live in Eastern North America and want to learn your bird songs, I recommend it to you.