Birds could be considered animals, yes. But the reason why the Animal Welfare Act isn't covering birds, is because they only help abused and mistreated animals, which I personally think they cover birds as well.
Birds are indeed animals. I don't why they aren't covered by the AWA, but you can write to your state legislator to have the laws changed or modified by getting a bunch of signatures to send along with a polite letter outlining your concerns. http://www.idausa.org/facts/awafacts.html
Yes birds are animals. It's possible that they're not covered because so many of them cross national boundaries during migration. Without a consensus of the countries involved legislation here is almost useless.
The USDA interprets the act to currently exclude birds, all cold-blooded animals (e.g., reptiles), rats and mice bred for research, and horses and other farm animals such as cows and pigs, used or intended for use as food or fiber. Horses and other farm animals are covered if they are used in experiments, but equine animals are specifically denied coverage if they are used in entertainment events. There are no regulations that govern the conduct of an experiment or what the animals will be forced to endure during an experiment.
The Animal Welfare Act is the federal law that governs the humane care, handling, treatment and transportation of some animals in certain situations: animals in laboratories, dealers who sell animals to laboratories, animal exhibitors, carriers and intermediate handlers, dog and cat breeders, puppy mills, zoos, circuses, roadside menageries and transporters of animals. The Animal Welfare Act does not protect animals during an experiment, regardless of how painful or even unnecessary it is. Excluded from the act are the following: retail pet stores, state and county fairs, livestock shows, rodeos, purebred dog and cat shows and "fairs and exhibitions intended to advance agricultural arts and sciences."