Separate it from them. You can't put ducks that haven't brooded together and expect it to be love at first sight. Even with ducklings it takes them awhile to get use to the intruder umm new one. Put it in a clear plastic brooder where they can see each other but the older ones can't pick at it. If you do it slow they will eventually get alongI just got another ducklings today, and the older ducklings are picking on it, what can I do?!