For My Goodness readers out West seeking an animal experience, there's the San Diego Zoo, where for $150 (scholarships available), you can join the Conservation Corps for ages 14-18, learn wildlife lore, and then make presentations to the public. The San Diego Zoo has plenty of education programs, including an appealing art camp for fourth-graders all the way up to adults.
National conservation groups, notably the Audubon Society, offer classes and family weekend outings during which you and your son would learn about how ecosystems work, as well as how to tell a sparrow from finch.
Your son is at a great age to talk about how human beings sometimes treat animals carelessly and why pets can end up abandoned. So direct him to the Humane Society's kids' Web site, where young people can learn how to lobby their representatives to ensure the humane treatment of animals and fundraise for their furry friends. He's also at a good age to learn the interesting ways in which animals can be helpful to people.
There are animals that you couldn't bring home to your apartment under any circumstances, but from which human beings can derive great benefit. Take a look with your son at the University of California-Davis Veterinary School Web site for information about equine therapy for people with mental or physical challenges. There's a program not far from where you live. I bet they wouldn't mind having you come observe; it's a very cool thing to watch. Kids and adults gain strength, balance, and confidence from riding—even simply from being around—horses. There's nothing as wonderful for a kid as asking a horse to move over, giving the animal a gentle shove with a hip or shoulder, and having the 2,000-pound beast move as ordered.
Good for you for picking up on your son's interest and encouraging it. As a bonus, your query has led to my own wonderful discovery: There exists in the world such a thing as elephant-assisted therapy.