Did you know that chickens have better colour vision than we do?

Look deep into the eye of a chicken and you will find a masterpiece of biological design, according to a paper published in PLoS One, an online journal of the Public Library of Science. The organisation of light receptors in the retina of a chicken apparently exceeds that seen in most mammalian retinas.

Researchers at Washington School of Medicine in St Louis have mapped five types of light receptors in the chicken’s eye. They discovered the receptors are laid out in interwoven mosaics that maximise the chicken’s ability to see many colours in any given part of the retina.  

The researchers say that birds may owe this superior colour vision to not having spent a period of evolutionary history in the dark, unlike mammals, which are thought to have been nocturnal for millions of years. As a result, say the researchers, birds have more types of cones (the receptors responsible for daytime vision) than mammals.

The human retina has cones sensitive to red, blue and green wavelengths, while bird retinas also have cones than can detect violet wavelengths as well as a specialised structure pigmented to filter out all but a particular range of light. This extra sensitivity to colour may help birds in finding mates, which often involves detecting colourful plumage, or when feeding on berries or other colourful fruit.

These findings could also have a practical relevance for human beings in that they could help in the use of stem cells and other new technologies being investigated to treat the 200 or so genetic eye disorders. Many of these disorders affect the cones and rods and can cause various forms of blindness in the human eye.