Date:July 12, 2016
The ability of finches, sparrows, and many other birds to see a visual world hidden to us is explained in a study published in the journal eLife.
Birds can be divided into those that can see ultraviolet (UV) light and those that cannot. Those that can live in a sensory world apart, able to transmit and receive signals between each other in a way that is invisible to many other species. How they unlock this extra dimension to their sight is revealed in new findings from the Washington University School of Medicine in St. Louis.
The study reveals two essential adaptions that enable birds to expand their vision into the UV range: chemical changes in light-filtering pigments called carotenoids and the tuning of light-sensitive proteins called opsins.
Birds acquire carotenoids through their diets and process them in a variety of ways to shift their light absorption toward longer or shorter wavelengths. The researchers characterized the carotenoid pigments from birds with violet vision and from those with UV vision and used computational models to see how the pigments affect the number of colors they can see.
"There are two types of light-sensitive cells, called photoreceptors, in the eye: rods and cones. Cone photoreceptors are responsible for color vision. While humans have blue, green, and red-sensitive cones only, birds have a fourth cone type which is either violet or UV-sensitive, depending on the species," says senior author Joseph Corbo, MD, PhD, Associate Professor of Pathology and Immunology.