This common wood pigeon (Columba palumbus) and sibling did not make it past their embryo stage of development. The broken eggs were found this morning shortly after falling from the nest.
Eurasian jays may be to blame: these large birds are particularly active and efficient predators in the area. It is common to see them fiercely hunting down great tit and blue tit fledglings, and just two mornings ago, a couple of them visited the pigeon nest the eggs fell from. They quickly left because one of the parents was incubating the eggs, but must have kept a close eye on the nest. Magpies could also be responsible.
Established for the domestic pigeon (Columba livia domestica), the above table of development (link to full size image) shows that the embryo was quite advanced and only had little time left before hatching.
Location: Bayreuth, Germany