Birds Evolved Ultraviolet Vision Multiple Times: Not Just Black and White

How often have birds evolved ultraviolet vision? It's not just one. Using a phylogenetic analysis of the evolution of violet sensitive and ultraviolet sensitive vision in modern birds, researchers were able to find out exactly how many times this feature appeared.

Birds use their color vision to help select mates, hunt, forage for food and spot predators. Although previously scientists believed that ultraviolet vision arose only one time in birds, this new report shows that, in fact, it has arisen far more often.

Published in the journal BMC Evolutionary Biology, the researchers examined the eyes of modern daytime birds. All of them have either violet sensitive or ultraviolet vision that involves the genes responsible for producing the light sensitive pigment, SWS1 opsin. By sequencing this pigment from 40 species of birds in 29 families--everything from the cokatiel to the whitebearded manakin--the researchers found that the pigment changed at least 14 times over the history of modern day birds. How exactly did they sequence the pigment? They extracted DN from the bases of feather quills, blood, muscle or other tissue. They then reconstructed the proteins that made up the light-sensitive pigments in the birds' eyes.

Yet birds don't see color in the same way as humans. We have three different color receptors, or cones, that are sensitive to light of different wavelengths. These mix together in order to reveal all different shades of color. Birds, however, have four cones-essentially they are able to see more colors than humans can.

The change itself from violet sensitive to ultraviolet is surprisingly simple, according to researchers. It only takes a single mutation in the DNA sequence to occur. Scientists are unsure why bird lineages switched between back and forth between these two types of color sensitivity. However, they hypothesize that it could have to do with attracting mates while still evading predators.