Hummingbirds can see the color 'invisible'

With four cone-shaped cells, the broad-tailed hummingbird can detect colors outside the visible spectrum of humans, the new study says.

These are colors that do not belong to the spectrum or a rainbow-like color band. The human eye with 3 cones can only see one color outside the spectrum, which is purple.

The purple (with a range between red and blue) does not appear in the rainbow range but we can see it is due to the two cone cells corresponding to the short wave blue light and the long wave red light triggered. like at the same time.

However, the hummingbird eye has a separate cone cell that recognizes this color, according to research published in the Proceedings of the National Academy of Sciences on June 22. Visions with their four cones are called tetrachromacy .

"Biologists have long thought that some birds can distinguish more colors than humans, but our study is the first to confirm that is the case for hummingbirds , " the author said. Researcher Mary Caswell Stoddard, associate professor of ecology and biological evolution at Princeton University, said. 

Male broad-tailed hummingbird. (Photo: CNN).

Stoddard and his colleagues used the Rocky Mountain Biological Laboratory in Gothic, Colorado to set up outdoor tests of broad-tailed hummingbirds. The research process takes place throughout the summer and continues for three years.

They use custom LED devices to display two different colors on round surfaces, next to different food sources. One good source of food for hummingbirds - called rewards - is sugar water, for example, while the rest contains only plain water.

Before dawn, the team placed an LED light next to each food source. Each tube emits a different light. They often change the position of the colored tubes and every time so, the hummingbirds quickly identify which color is related to the reward after only a few hours.

LED tubes have displayed a wide range of colors including non-spectral colors such as a UV + green mixture, which is how researchers identify the light components that hummingbirds can see. see.

Research results show that the broad-tailed hummingbird can detect non-spectral colors and mixtures, such as purple, ultraviolet + green, ultraviolet + red and ultraviolet + yellow. They can even distinguish two different UV ultraviolet compounds, or between them and the original color components.

"I was thrilled to see birds learning how to distinguish two different colors, but they look identical in our eyes," Stoddard said. " Hummingbirds are intelligent. They learn to associate color with food very quickly. This ability helps them identify which flowers have sweet nectar through color."

The researchers analyzed a total of 3,315 different colors from animal and plant hair, then came to the conclusion that 30% of the feathers and 35% of the plant colors seen by hummingbirds were non-spectral colors. .

"The color we saw in the field of wildflowers at the research site was really impressive. But in the eyes of a hummingbird supermarket, the sight was definitely even more brilliant," said David Inouye, Former Professor of biology at the University of Maryland College Park, co-author of the study.

The ability to recognize a variety of colors is important because it provides information about mates, predators and food sources. The team's new finding is therefore very useful in preserving hummingbirds.

"We are studying how hummingbirds use colors to find flowers and impress their mates, and see how these behaviors can be affected by climate change," Stoddard added.