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The plumage of white barn owlsTyto alba) appears to be a unique evolutionary quirkMicrotus arvalis), their key prey.
Although the nocturnal owls can not camouflage themselves under bright moonlight like their brown counterparts, their white feathers reflect the light, exploiting the rodents' aversion to "flash" lights and causing them to freeze for longer.
The research, published in the journal Nature Evolution & Ecology by Luis San-Jose and Alexandre Roulin from the University of Lausanne, Switzerland, and collaborators, was drawn from 20 years of data and follow-up studies.
But it was not what they were initially looking for.
"One day we had something in front of the eyes for decades," Roulin says. It dawned on them that the barn owl is the only white nocturnal predator, which is "totally counter-intuitive", he adds.
"This appeared weird at first sight. And we thought, during full moon nights, we are flying stars in the sky, very visible. "
When rummaging through the data, they found that their plumage coloring, breeding success and foraging activities matched with the cycles of the moon.
To explore reproductive biology, they analyze data on brood size, nestling body condition and survival and parental feeding rate, along with online information on moon cycles.
Results showed that the full moon has been negatively impacted on the owls but positively on white owls.
"From new-to-full-moon nights," Roulin explains, "nestlings survived when the parents were white but the parents were red."
To investigate hunting behavior, they attached GPS tags to the back of adult barn owls. Revealedls .ls .ls .ls .ls .ls .ls .ls .ls .ls .ls .ls .ls .ls .ls .ls .ls .ls .ls .ls .ls .ls .ls .ls .ls.
Finally, to illuminate the behavior of the audience, the researchers have taken a closer look at the fact that they could only have a full moon.
To test the rodents' startle response, they succumbed to the clueless mammals to red and white stuffed barn owls flying on a zip wire.
This was most revealing.
"We found that voles 'panic' much more when they are attacked by a white than a red owl," says Roulin, "but only under full moon conditions, not under new moon conditions.
"We were able to demonstrate that the plumage of white light reflects the triggers of fearful reactions in the prey." Because the voles froze, they were easier to catch.
The findings were strong and consistent across all analyzes, and it was possible for this reason to explain why white barn owls, which is predominate around the world, have an evolutionary advantage.
"Our results can help explain the evolution and maintenance of color polymorphism, that is, the presence of different colored individuals in a single population," Roulin says.
This suggests the moon influences the evolution of nocturnal animals' color patterns while the sun shapes that of diurnal creatures, he adds.
Bird ecology and evolution expert Jesús Avilés, from EEZA-CSIC in Spain, writes in an accompanying paper that the findings are "exciting".
Although the moon is known to many forms of behavior, Avilés explains.
He suggests that the prediction and prediction of moonlighting be observed simultaneously – and under natural conditions – to fully grasp the adaptive significance of owl plumage patterns.
The Royal Institution of Australia has an education resource based on this article.
You can access it here.
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