Spectacular bird's-eye view? Hummingbirds see diverse colors humans can only imagine

Team trains wild hummingbirds to discriminate UV color combinations

Date: June 15, 2020

Source: Princeton University

To find food, dazzle mates, escape predators and navigate diverse terrain, birds rely on their excellent color vision.

"Humans are color-blind compared to birds and many other animals," said Mary Caswell Stoddard, an assistant professor in the Princeton University Department of Ecology and Evolutionary Biology. Humans have three types of color-sensitive cones in their eyes -- attuned to red, green and blue light -- but birds have a fourth type, sensitive to ultraviolet light. "Not only does having a fourth color cone type extend the range of bird-visible colors into the UV, it potentially allows birds to perceive combination colors like ultraviolet+green and ultraviolet+red -- but this has been hard to test," said Stoddard.

To investigate how birds perceive their colorful world, Stoddard and her research team established a new field system for exploring bird color 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 color vision experiments.

"Most detailed perceptual experiments on birds are performed in the lab, but we risk missing the bigger picture of how birds really use color vision in their daily lives," Stoddard said. "Hummingbirds are perfect for studying color vision in the wild. These sugar fiends have evolved to respond to flower colors that advertise a nectar reward, so they can learn color associations rapidly and with little training."

Stoddard's team was particularly interested in "nonspectral" color combinations, which involve hues from widely separated parts of the color spectrum, as opposed to blends of neighboring colors like teal (blue-green) or yellow (green-red). For humans, purple is the clearest example of a nonspectral color. 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 color -- purple, birds can theoretically see up to five: purple, ultraviolet+red, ultraviolet+green, ultraviolet+yellow and ultraviolet+purple.

Stoddard and her colleagues designed a series of experiments to test whether hummingbirds can see these nonspectral colors. Their results appear June 15 in the Proceedings of the National Academy of Sciences.

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Color vision makes birds of prey successful hunters

Date:  August 29, 2018

Source:  Lund University

In many cases it is the colour of the prey that helps predatory birds to detect, pursue and capture them. In a new study, biologists at Lund University in Sweden show that the Harris's hawk has the best colour vision of all animals investigated to date -- and in certain situations, even better than humans. The findings may help to protect threatened birds of prey against hazards such as wind turbines and power lines.

"It's fascinating. I did not think that colour vision would be of such significance, rather that birds of prey simply have better visual acuity than humans and that was the reason they detect objects so early and at a great distance. However, colour is of considerable importance," says Almut Kelber, biologist at Lund University.

Normally, the size of the eyes determines optical resolution and thus what people or animals can see. The bigger the eyes, the higher the resolution. The size of the eyes in turn is usually linked to body size. Large body, large eyes; small body, small eyes. Particular to birds is a poor ability in general to see contrasts between different objects. Their contrast vision is almost ten times lower than ours.

However, there are exceptions, and the Harris's hawk (Parabuteo unicinctus) is one of them. The study by the Lund biologists shows that if an object is not distinguishable from the background and the colour is approximately the same, it is more difficult for a bird of prey than a human to detect it. If, on the other hand, the object has a different colour than the background, the Harris's hawk can detect it at twice the distance compared to human vision.

"It's exciting! The hawk weighs less than one kilo and has small eyes. Nonetheless, it can see many times better than us, even though it is so small and light," says Simon Potier.

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Female color perception affects evolution of male plumage in birds

Date:

November 25, 2014

Source:

University of Chicago Medical Center

Summary:

The expression of a gene involved in female birds' color vision is linked to the evolution of colorful plumage in males, reports a new study. The findings confirm the essential role of female color perception in mate selection and sexual dimorphism.

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