I grew up in a rural area and became accustomed to a chorus of birds coaxing me out of bed in the mornings. While never introduced to proper bird watching, I do enjoy my fair share of observation and listening. Here's a wonderful resource to acquaint yourself (or your children or students) with the chirps and their composers: "Common Birds and their Songs" by Lang Elliott and Marie Read includes descriptions, full-page photos, and audio tracks for fifty common birds in North America. It's an incredible resource!
You can also find this book in the Michael Olaf's "Child of the World" catalog. I can't recommend it enough! It will certainly be put to use in my classroom this coming school year.
Thanks for reading :)