One of the fascinating traits of birds, and shared with their theropod dinosaur ancestors, is the external development of their offspring. In all 10,000 bird species the fertilised embryo develops in the egg outside the female's body. Often the egg is laid in a nest built by the parents, and may be one, or one of many in a clutch. The avian eggshell is a complex bioceramic which protects the embryo during development from physical damage, facilitates gas exchange, and provides calcium for bone growth.

Most birds lay immaculate white eggs, but not all. Why do some species lay coloured, and/or exquisitely patterned eggs? We know that eggshell pigmentation is particularly important for ground-nesting species, which camouflage their eggs, and for species parasitized by brood parasites. However, the association between the colourful eggshell and the light transmitted through the shell, and to the chick inside the egg, is much less well established. What if the colour of the eggshell was specific to a particular birds’ nest-type, and could influence how quickly the chick develops, whilst at the same time protecting it from harmful UV-wavelengths? We think it can!


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