It is illegal to pick up dead birds, and eggs. I don't know what the penalty is; I don't think you'd be arrested; they might fine you if they wanted to be jerky about it. I believe the reason for the laws are actually to protect wildlife; you know, so people don't take eggs out of nests, or shoot wild birds just so they can have them stuffed and mounted for decoration. If you want to you could call your local wildlife rehabilitator, most states have lots of them, and tell them what you are doing; they would probably work with you on it. Anyway, it'll be fun to find out what it is.