A couple of other things I have my eye on:
I will also put in some field guides we have as well as a new camera for him to use when we go on walks--as soon as I can walk for more than ten minutes without having to go pee. Also coming up, our library will be hosting a pigeon day, and later this week the parks department is hosting a series of nature walks downtown.
If you are interested in going deeper, Heather posted a great link to the Cornell Lab of Ornithology as well as a robin unit study we may have to try next spring. Also, Ami has several great resources over at HomeschoolShare: a Backyard Birds Lap and Note, Storks, Ostriches, and Eagles, just to name a few. And of course there are great FIAR books with birds like Owl Moon and Make Way for Ducklings.