Among 20 nests of Common Buzzards, found in 1996 in SE-Drenthe, two clutches of 4 eggs were found. In one of these, produced by a pair in adult plumage, two eggs did not hatch. The other two eggs hatched and fledged. One of the unhatched eggs contained a full-grown embryo with two heads (see Photo). Both heads were fully developed, including an egg-tooth on the bills. The egg-shell did not show signs of attempts to open it from the inside.