Chennai: A latest study has found that better colour vision helps birds find food, dazzle mates, escape predators and navigate diverse terrain. They are far superior to humans at detecting differences between two similar colours.
To investigate how birds perceive their colourful world, Mary Caswell Stoddard, an assistant professor in the Princeton University Department of Ecology and Evolutionary Biology and her research team established a new field system for exploring bird colour vision in a natural setting.
Working at the Rocky Mountain Biological Laboratory (RMBL) in Gothic, Colorado, the researchers trained wild broad-tailed hummingbirds (Selasphorus platycercus) to participate in colour vision experiments.
“Mary Caswell Stoddard, an assistant professor in the Princeton University Department of Ecology and Evolutionary Biology,” says Stoddard.
Humans are trichromatic, which means they have three types of colour-sensitive cones in their eyesâattuned to red, green and blue lightâbut birds have a fourth type, sensitive to ultraviolet light. So birds are tetrachromatic.
She added: “Not only does having a fourth colour cone type extend the range of bird-visible colours into the UV, it potentially allows birds to perceive combination colours like ultraviolet + green and ultraviolet + redâbut this has been hard to test.”
“Most detailed perceptual experiments on birds are performed in the lab, but we risk missing the bigger picture of how birds really use colour vision in their daily lives,” she said further.
Stoddard added: “Hummingbirds are perfect for studying colour vision in the wild. These sugar fiends have evolved to respond to flower colours that advertise a nectar reward, so they can learn colour associations rapidly and with little training.”
Her team was particularly interested in “nonspectral” colour combinations, which involve hues from widely separated parts of the colour spectrum, as opposed to blends of neighboring colours like teal (blue-green) or yellow (green-red). For humans, purple is the clearest example of a nonspectral colour. Technically, purple is not in the rainbow: it arises when our blue (short-wave) and red (long-wave) cones are stimulated, but not green (medium-wave) cones.
While humans have just one nonspectral colour, purple, birds can theoretically see up to five: purple, ultraviolet + red, ultraviolet + green, ultraviolet + yellow and ultraviolet + purple.
Stoddard and her team designed a series of experiments to test whether hummingbirds can see these nonspectral colours. Their results appeared on 15 June in the Proceedings of the National Academy of Sciences.