Scientists solve mystery about hunting owl color

Flying slowly and silently through the night sky, the barn owls They are majestic nocturnal hunters who successfully capture rodents that move along the ground below. You Scientists have long been intrigued by a trait that would apparently harm the bird during its midnight hunts. .

The plumage on its underside and wings is gleaming white, an unusual feature that, in theory, should make it difficult for the owl to approach its prey without being detected.

Unlike the snowy owl, the barn owl lives in latitudes where it does not snow regularly. The barn owl’s paradoxically bright plumage intrigued biologist Juanjo Negro and his colleagues, who thought the challenging biological phenomenon deserved further investigation.

“We started with the intuitive feeling that the barn owl’s exceptional whiteness is so shocking that it must imply some adaptive advantage,” said Negro, a research professor at the Doñana Biological Station-Spanish National Research Council in Seville, Spain, by e-mail.

Previous searches from September 2019 had suggested that the bright white coloring was essentially a form of shock and intimidation, exploiting the rodents’ aversion to bright light. By making the predator more visible to rodent prey, which freezes in fear, the owls’ whiteness made the voles easier to kill, the previous study found.

The latest research by Negro and his team suggests instead that the barn owl’s bright white plumage is actually a form of nighttime camouflage or counterlighting that gives the hunter an element of surprise.

Barn owl feathers match the moon’s light

The bird’s reflective white underside effectively mimics moonlight, according to the new study describing the team’s findings, published in the journal PNAS this Monday (16).

The bright plumage allows its silhouette to blend into the night sky and makes it difficult for mice or other rodents to detect the owl. “When the Moon is visible, the sky has some brightness that varies depending on the direction of observation. Under these conditions, a dark bird would be seen by its potential prey as a black silhouette against the sky,” said Negro, lead author of the study.

“But if the ventral part of the bird is reflective enough, in other words, if it is ‘white’ enough, it would reflect a good portion of the Moon.”

According to the researchers’ calculations, the contrast between barn owls’ white, reflective undersides and large areas of the illuminated night sky falls below the detection threshold of the rodents’ visual acuity, allowing barn owls to approach prey from a few meters away, from a wide range of directions, without being detected.

“This explanation has not been proposed before to justify the whiteness of barn owls,” Negro added.

A similar phenomenon exists in the ocean, where fish often have clear undersides to match the sunlit water and make them less visible to predators hovering in the depths below.

However, not all barn owls have white bellies; some have reddish-brown plumage. Negro said the research did not investigate hunting success in relation to plumage color, but previous research had suggested that whiter barn owls were more efficient hunters than their darker counterparts during the full moon.

Bright white vs. concealment

Barn owl expert Alexandre Roulin, professor of biology in the department of ecology and evolution at the University of Lausanne, who led the previous research suggesting that the species’ white coloring shocked and immobilized its prey, said he was not entirely convinced by the new explanation. However, he said he couldn’t ignore her.

“We don’t want to dismiss the authors’ hypothesis immediately. In fact, it may be complementary to ours. Perhaps at long distances the white plumage helps with camouflage, while at close range it may serve to make the owl more visible,” he said in an email.

One key aspect that Roulin said needed further explanation was the behavior of field mice under moonlight. “We observed that field mice remained motionless for longer when the approaching owl was white rather than reddish. Previous research has shown that this immobilization is an anti-predator response,” Roulin said.

“Based on this, we can argue that the rodents recognized the snowy owl as a predator, suggesting that the owl was visible rather than camouflaged,” said Negro, adding that the owl’s ability to fly in complete silence, a trait that helps to approach prey stealthily, it does not match the idea that the predator would want to become more visible. However, he agreed that the new hypothesis does not fully refute the previous theory.

Camouflage is often considered a daytime phenomenon based on light and shadow. Negro said there are likely other forms of animal coloration that serve as nighttime camouflage, something that has not been as well studied as daytime concealment tactics.

“Nocturnal ecology is an emerging field, and considering that half of the planet’s animals are essentially nocturnal, adaptations to the Moon’s natural cycles are certainly widespread,” he said.

This content was originally published in Scientists solve mystery about hunting owl color on the CNN Brasil website.

Source: CNN Brasil