How can I tell if my duck is being picked on by my other ducks?

[chnn90]

So I have four ducks (all female) and recently I've noticed that three of them have been picking on one of them. They've been nipping at her and she's always in the back of the group when they move around. She's usually outside of the group when they forage too. She also hasn't been laying (we think) and she's been loosing a lot of feathers too. At first she was just loosing little feathers then she started loosing more mature feathers (and a lot at one time). Is she sick or are the others just picking on her for some reason? And if they are picking on her, what can I do to make them stop?

 

[17 chickens]

Do you have a drake? If not it might help to distract them from picking on her. You could all so move her to another pen and then find the next bottom of the ducks then move that one in with her.