I have a pair of mallard ducks that started coming into my yard this spring. Started feeding them corn and offering them water. The male no longer comes but the female does daily for a bath in a 3 gallon bowl and to eat. My question is when I got home today I found pieces of eggs shell in the water bowl and a dead duckling. I think some yoke was in the bottom of the bowl also. The bowel is 3 or 4 inches tall so I have no idea how this happened. I do have other bird feeders out so other birds visit as well. Can anyone explain this? Thanks!