Hi Cody, I used to have the Rebel XTi; it's a great camera and with that lens you should definitely be able to photograph some birds. You'd have to be awfully close to a warbler to get a good shot, but definitely worth the try. You will get good shots of ducks, herons, etc. I find the raptors to be difficult to get very close to for a good picture. However, if you're out a lot, you are bound to run into some great picture situations. I've found over time, you get better pictures staying still and waiting for the birds to come to you.
Are you interested in butterflies/dragonflies at all? You could probably get some good pictures of them as well.
I hope you enjoy your new purchase and look forward to your pictures.