Weird bump on ducklings bum!!!

[Reyanna_]

So I got some White Pekin Ducklings recently all are fine but one it has this weird bump on his rear and he pull all of his down off of it! Does anyone know what this is?? Please help im concerned ab the little guy.

 

[FoodFreedomNow]

Is it on his back, near his tail? If so, it may be a blocked uropygial (also called "preen" or "oil") gland. You may find this thread helpful - warm compresses may help "unblock" it. More info here from DuckDVM.