I have a friend who I have been hatching ducks with. one of her new ducklings (cayuga) (about a week old now) seems to act normal, but at times get up on its "toes" and then tip backwards and then not be able to right itself. It is fed duck food not chicken starter. it is still under the lights so it is container in a smaller area . there are a total of 5 ducklings. any suggestions as to what the issue might be?