29 July 2014 Last updated at 02:17
By Michelle Warwicker
The eggshells of wild birds may act like "sunblock", scientists have said.
A range of UK birds' eggs showed adaptations in pigment concentration and thickness to allow the right amount of sun to reach the embryos inside.
Researchers examined 75 species' eggs kept in a museum collection.
"Embryos do need UV exposure to develop - too little and they don't develop enough... too much and it causes damage," said team member Dr Steven Portugal from the University of London.
"Birds whose nests are exposed to the sun and birds which have long incubation periods too, have more pigment and allow less light to go through the shell to avoid UV damage to embryos," he explained.
The study, published online in the journal Functional Ecology, suggests thickness and pigment in eggshells change depending on the nest environment.
Wild birds' eggshell colours can be white, blue and spotted. The blue colour found in many eggs is caused by a pigment called biliverdin, while dark spots are produced by a darker pigment, protoporphyrin.