Need your help! Gosling plucked itself!

[kees]

I have a 3 week old Sebastopol gosling. He has been eating Crumble and water. His behavior has been loving and inquisitive. However, there's a patch of skin by the right wing where he's plucked himself down to the skin! I examined him and there appear to be no mites or other insects. The gosling has been in contact with 5 other Runner ducklings that came from Metzer Farms. All of the birds are the same age and none of the others bother the gosling or show any other symptoms. Can someone please help?

I can't post any pictures, but any help would be greatly appreciated before any more damage occurs.

Suzy