GESTATION PERIOD FOR SWAN EGGS SECRETS

I am no specialist on swans. I rather think that an evening-time predator filched the eggs. I've listened to people declare that their birds( chickens, geese, what ever) clear away infertile or nonviable eggs from their nest. In 40 many years I have not had a fowl take away their own individual egg/s from the nest other than unintentionally. luvsw