Where the hell are the swans?!

So, after about 40 days and 40 nights, the swan eggs finally hatched, as I mentioned before. Everything was going great, but when K checked the nest on Tuesday morning, the swans were nowhere in sight. Just an empty nest with some broken shells and one lone egg that never hatched. I checked this morning and they're still not there. So, what happened to them, I ask you!?