Diagnosing my Pekin ducks

[nbkfy93]

I had 4 ducks,two female and 2 males. Recently, we discovered that a male had died. We found him in the coop and thought that the two males had fought and had accidentally broken his neck. There was no visible injury. Now today,about 5 weeks later, we found a female sitting in the woods with neck stretching/flopping and she had been fine and foraging and swimming a few hours earlier..any ideas??Also no visible signs of trauma..One pair is 3 yrs old and the two with illness were 2 yrs old.