What can you learn about a bird if you only hear its song? Possibly quite a bit. For one thing, you can usually make good guesses about a bird's lifestyle and environment just by hearing a few seconds of birdsong.
For example, almost anyone will recognize the sound of sea birds, even though they are diverse. It could be that the screeching call is good at carrying over the sound of crashing surf.
Likewise, sparrows and finches and other woodland birds have a sharp chirp that may fit the more intimate environment of a thicket. This is in contrast to a hawk's piercing shriek, necessary at high altitudes in wide open spaces.
One of my new favorite web resources is Doug von Gausig's recordings on Naturesongs.com: http://www.naturesongs.com/birds.html He sometimes adds entertaining stories and vivid photos to his collection.
What I'm writing here about birds isn't complete or accurate. These are my own speculations about bird calls, but they tie in with a useful science learning technique.
How to Learn Biology in Multiple Modalities
Most experienced teachers understand that there are different ways of learning. Traditional schooling puts a heavy emphasis on textbooks and other reading, but many students learn better visually. A small handful of students are kinesthetic learners; they do best with models and other hands-on learning tools.
I try to include visuals in all my science teaching, and I add hands-on elements whenever possible. But audio is another way of learning, one which is underutilized.
I was fascinated a few years ago when I heard my own heart beating and blood flowing as part of a medical exam. I think students can be similarly impressed by hearing the sound of wind in different landscapes, crashing waves, and of course the natural calls of animals.
This is just one more way to take the material out of the textbooks and bring it to life. It can be the beginning of valuable discussions, like my speculation on the advantages of specific bird calls. Researchers have already taken note of the value of sounds.
As a tip on how to learn biology, using your ears can be almost important as using what's between them.