I am losing eggs just lately, not hatching ones, just in the nests. I have a feeling its magpies or crows, as they have nests in the trees, and I can hear the young squawking. Today for example, I am at least 10 eggs down, which is a lot, but I am sure the hens are laying. Rats too will take them, but I would guess at the birds. They are clever, and I have watched them listen for the hens to declare they have laid and then swoop down.