Having eyes like a hawk doesn’t make birds of prey better hunters.
According to a new study, it’s the color of the prey that helps predatory birds to detect, pursue and capture them.
Biologists at Lund University in Sweden show that the Harris’s Hawk has the best color vision of all animals investigated to date — and in certain situations, even better than humans.
Findings Help Protect Birds of Prey
The findings may help to protect threatened birds of prey against hazards such as wind turbines and power lines.
“It’s fascinating. I didn’t think that color 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, color is of considerable importance,” says Almut Kelber, a biologist at Lund University.
Typically, the size of the eyes determines the optical resolution and what people or animals can see.
The bigger the eyes, the higher the resolution. The size of the eyes is usually linked to body size. Large body, large eyes; small body, small eyes.
Birds have a poor ability to see contrasts between different objects. Their contrast vision is almost ten times lower than ours.
Harris’s Hawk an Exception
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 color 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 color 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.
Color Vision Key for Hunting Success
Up to now, research has not focused on the significance of color for the hunting success of birds of prey.
Researchers have considered that the color vision of animals has been most important at a relatively close range and thus for quite large objects.
Simon Potier and his colleague Almut Kelber show that colors are significant for enabling birds of prey to detect quarry at a great distance.
Good color vision is also particularly important in environments such as forests, where shadows, for example, can confuse visual impressions.
Seeing Uniform Color
In the study, researchers used tame Harris’s Hawks in France. A uniform color was projected on a large screen behind one of the perches, and a multi-colored grid pattern was displayed behind the other perch.
If the hawk chose the screen with a uniform color it received a reward, the other choice wasn’t a reward.
Once the hawks learned that a uniform color without a grid pattern meant a reward, the researchers gradually changed the grid pattern’s contrast and closed the distance between the grid lines until the hawk could no longer see the difference between the two screen images.
“The more fine-meshed patterns an animal can see, the sharper their visual acuity,” says Potier.
Protecting Threatened Birds of Prey
The findings may have practical importance for conservation, that is protecting threatened birds of prey from disappearing altogether.
“Once we understand how birds of prey perceive their world, we can help to improve efforts to conserve and protect them,” he adds.