New research reveals that hummingbirds have an addition of extra color-sensitive cones that enable them to see more colors than the human eye can see.
The researchers conducted an experiment on wild broad-tailed hummingbirds (Selasphorus platycercus) in Colorado. The findings suggest that they have the ability to discriminate non-spectral colors, including the ultraviolet wavelengths, which are invisible to a human's naked eye.
Their ability to see more colors play an important role in behaviors such as mating, feeding, and evading predators.
Why Do Hummingbirds See More Colors?
A human eye has three kinds of color-sensitive cone cells. These cells help human cells to perceive trichromatic color- made up of red, green, and blue light.
But hummingbirds have four types of cone cells that help them see and process the variety of different kinds of colors, according to Science Alert.
The trichromatic color helps humans to perceive the non-spectral color purple because it is the combination of blue and red. But animals with an extra cone can see an even greater spectrum of colors because they are more sensitive to more kinds of light wavelengths- composed of color combinations that humans cannot see or even fathom.
According to an evolutionary biologist, Mary Caswell Stoddard from Princeton University, humans are color blind compared to birds and many animals. Having an additional cone cells extend the range of bird-visible colors into the UV.
It allows birds to perceive color combinations which include ultraviolet+green, ultraviolet+yellow, ultraviolet+purple and ultraviolet+red. However, it has been hard to test what colors the birds actually see.
Testing the Bird Vision
Caswell and her team set up 'bird vision' LED tubes programmed to show many colors, such as the non-spectral colors to test what colors do birds really see. These devices were then placed beside water-feeders which contained sugar water next to one color, and other water-feeders that included plain water next to a different color.
The researchers would then swap the positions of the feeders and see if the birds could distinguish which feeder was which.
After three years and a series of experiments, the results showed that animals can easily distinguish between the different kinds of non-spectral colors to obtain a sweet reward- sugar water.
Study co-author and PhD student Harold Eyster from the University of British Columbia said that although the ultraviolet+green light and green light looked identical to the human eye, the birds correctly choose ultraviolet+green which is associated with sugar water.
The experiments showed a sneak peek to the world of the hummingbird. The color variations that the birds see might be hard for humans to understand.
The researchers also tried to do another experiment wherein they analyzed 1,000 different kinds of bird plumage and almost 2,400 different types of plants. They found that the colors of about one-third of the bird and plant were perceived as a non-spectral color.
There is still a lot to be learned in the experiment, with the impressive results of the experiment, it still falls short of proof that birds possess a tetrachromatic visual system.
"Humans are color-blind compared to birds and many other animals." New research by 2018 Packard Fellow Mary Stoddard reveals that to find food, escape predators and navigate terrain, hummingbirds rely on excellent color vision: https://t.co/ZOh08c0oYg @Princeton #PackardFellows — Packard Foundation (@PackardFdn) June 15, 2020