Up until now my ducks' poop has been light and watery. They free range in the yard and I never noticed poop anywhere. Suddenly (no recent change in feed) it's looking more like goose poop. More solid and formed. When it is watery, it's very dark and thick. They have not started to lay yet, although I did start them on some oyster shell recently. Free choice, could that be it? How do I get them back to that nice liquid-y poop that just disappears into the lawn?