Aug. 29 (UPI) -- According to a new study, some birds of prey can detect contrasts between objects at a greater distance than humans -- but only if the object is a different color than the background.
The research suggests color vision is essential to a bird of prey's hunting prowess.
"It's fascinating. I did not 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," Almut Kelber, biologist at Lund University in Sweden, said in a news release. "However, color is of considerable importance."
Throughout most of the animal kingdom, larger eyes correspond with higher resolution vision. And larger eyes correspond with larger bodies. Bigger animals, like humans, tend to have higher resolution vision.
Harris's hawk, Parabuteo unicinctus, is an exception. Vision tests showed humans were better able to distinguish between objects with the same colors, but the Harris's hawk was able to see differently colored objects from farther away.
"It's exciting! The hawk weighs less than one kilo and has small eyes," said Lund researcher Simon Potier. "Nonetheless, it can see many times better than us, even though it is so small and light."
Scientists tested the birds, sometimes called bay-winged hawks, by having them fly to one of two faraway perches. Color patterns were displayed behind each perch. If the bird flew to the display with uniform color and no grid pattern, the bird received a reward. Once the bird was trained to recognize the uniform color display, researchers moved the bird farther and farther away, until the bird's behavior proved it could no longer distinguish between the uniform color display and the multicolored display.
Until now, scientists thought color vision was only useful to birds of prey at close quarters. But the latest findings -- published this week in the journal Proceedings of the Royal Society B -- suggest color vision is essential to the long range vision of birds of prey like the Harris's hawk.
Color vision is especially important in forest environments where shadows can easily be confused with prey. Understanding a bird's vision capabilities can allow scientists to better understand how birds interact with the environment.
"Once we understand how birds of prey perceive their world, we can help to improve efforts to conserve and protect them," Potier said.