From the almost perfectly spherical eggs of the brown hawk owl to the pointy eggs of the sandpiper, there is a surprising variety in the shape of bird eggs. Yet why birds lay different shaped eggs has remained unanswered, until now. It seems that the shape of an egg is not determined by the environment in which the adult lives, but instead by how it flies. There have been many drivers suggested to explain the differences in egg shapes seen across the avian world. A popular one posits that the shape is dictated by where the bird nests, using those birds that set up shop on cliffs as the perfect case. Some sea birds have eggs that are incredible pointy, for example, meaning they roll in a tight circle. This has been argued to be an adaptation to prevent them rolling off the cliff. Yet now it seems that this shape may instead be dictated by how much the species flies. By studying the shapes of over 50,000 eggs from 1,400 different species held in museum collections, the researchers were
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