Found these laying under a hibiscus bush in our garden, essentially in the middle of the lawn. They seem too big for all birds I've seen around here - blackbirds, sparrows, minah birds, starlings, wild parrots, but not big enough to be duck eggs, who I have seen about half a KM away. My only suggested theory is that a hedgehog rolled them there after stealing them from the nest of a hairy mammoth.