Broody hens

[Meca]

I have a few broody hens. I put four duck eggs under one of them. Today is day 21. So far she pecked one, one has completely disappeared, one was developing and it doesn't look like it's developing anymore and the last one looks like it still might be viable.

My questions are why would she peck one egg? The one that disappeared still has me baffled but my thought is she ate it.

And what are the chances of her hatching the last one?

 

[Meca]

This is my first experience with hatching anything.

 

[Meca]

It appears that she is eating the eggs. :-( I found another one gone but the last remaining egg looks like it might have yoke on it.

I am disappointed that she (or something is eating the eggs). Now, for the new question if she was eating them how do I get her to stop?