I have a female duck that when she trys to stay witht he others she starts staggering and falling over...I am not sure what is causing this and she eats fine when she gets to the feeder...She will start walking and fall over and the get up and fall over again to the point to where she will just sit still for a while and then try again...she is better in the mornings and it seems to get worse as the day goes on..I hate to see her struggling so hard and dont know what is wrong ..any suggestions as to what is causeing this? Thanks