If you have something taking nectar from a flower or your hummingbird feeder, but it is not a hummingbird, it probably is a Hummingbird Moth. This is the adult stage of the hornworm that is often found eating tomato leaves. In the adult stage, it will drink from hummingbird feeders and flowers just like a hummingbird. They can hover and fly backwards just like a hummingbird.
Reference(s):
