Originally Posted by Bleenie
I don't think it's healthy for any animal to eat any kind of poo.
I don't usually disagree with Bleenie, but I disagree with the above quoted statement. Manure from some animals is quite nutritious for ducks. We use ducks as part of our organic pest management system on the farm. They dabble in the cow pies. Not only do they break them up, but they also eat any of the parasites in all their various stages that reside in the manure. This disrupts the parasite cycle in our cattle, as well as keeps the fly population to a bare minimum during fly season. When I let the pasture ducks out in the morning, the first thing they do is go find all the fresh manure piles. It is sort of disgusting, but that is why I keep them near the manger. I do admit that last year when they finally discovered the huge manure composting area and spent all day doing nothing but foraging through the manure soup it produces, I couldn't stand it. It took several attempts, but I did finally manage to find a way to keep them out of the pile... they were persistent though!
With that said, chickens and ducks share some of the parasites and I would be concerned if your duck is eating a lot of chicken poop since she could be infecting herself. It could be something as simple as your duck seeing something moving, poop falling from the behind of a chicken, and she thought, "oh, this may be yummy," and after a few times she'll understand that nope it's not something yummy but just poop. I know I've seen a lot of our poultry go through this, but they eventually learn not to fall for that trick. Or it's as Bleenie suggested and she's lacking something from her diet.
I wouldn't be too concerned unless it's something she starts doing a lot.