Dead Hatchling

[Mallard Lvr]

I have a pair of Mallard ducks that have been visiting my yard since beginning of spring. I have corn and a water bowl out for them which they have been using. I don't see the male any more but the female comes daily to eat and take a bath in the water bowl. Yesterday I came home from work and noticed the water bowl looked very dirty. Upon closer inspection I found pieces of egg shell and a hatchling dead in the bottom. It was not still pink skinned it was probably close to hatching. There was also yoke in the bottom of the water bowl. The bowl is 3 or 4 inches deep and holds 3 gallons of water. I am new to this but have been feeding other wild birds that come to your backyard for years. Does anyone know the explanation of what happened here? Any replies welcome. Thanks!