Under a full moon the white plumage of barn owls triggers their prey to freeze for a longer time, thereby making the prey easier to catch, according to a paper published online this week in Nature Ecology & Evolution.
Moonlight changes the activity of patterns of animals as it alters an individual’s capacity to spot food or remain concealed. The moon also exposes night life to a variation of light, which may also drive the evolution of the colouring of nocturnal animals.
Alexandre Roulin, Luis San Jose and colleagues used GPS trackers to monitor the hunting success of red and white barn owls under different phases of the moon. They found that, although the white owls were more easily seen by their prey on moonlit nights, they were more successful at hunting rodents than the reddest owls, who could remain camouflaged.
To determine why the white owls were more successful, the authors flew taxidermied owls on a zip wire to measure the startle response of voles, the barn owl’s main prey. The authors observed that the light reflected off the white owls' feathers, which exploited the voles’ natural aversion to bright light. The voles froze, which could allow the owls to capture them more easily.
The authors suggest that this phenomenon may explain the persistence of both types of barn owl plumage. White barn owls are only favoured under certain conditions, such as under a full moon. Outside this scenario, the owl’s white plumage allows them to be easily detected by harassing competitors, such as carrion crows.