Birds use colour to identify eggs of other birds and eject them from their nests, research suggests.

Researchers at The University of Auckland have studied the habits of song thrushes in New Zealand and Europe and how they recognise their own eggs. The research has shown birds recognise small changes, particularly in the ultraviolet wavelengths, to distinguish between their own eggs and eggs of ‘parasite’ species, such as cuckoos.

The research was published online in Biology Letters.

The study introduced eggs into the nests of song thrushes, painted in a range of colours close to the bird’s own eggs. The study showed the birds ejected eggs of different colours from their nests, particularly those with differences in reflecting ultraviolet or short (blue) wavelength light.

"Birds have very different visual senses to humans, for example they can see ultraviolet wavelengths where we cannot," says Dr Mark Hauber of the School of Biological Sciences. "Those birds which parasitically introduce their eggs into the nest of other birds dramatically increase the amount of time and energy needed to provision the nest. Our research shows that the peculiar abilities of birds to perceive broad-spectrum colour is vital to recognise their own eggs, and can identify small differences and wavelengths that humans wouldn’t be able to distinguish."

The research was a collaboration with Drs. P. Cassey, University of Birmingham (UK), M. Honza, the Academy of Science of the Czech Republic and T. Grim, Palacky University (Czech Republic).