On Moonlit Nights, Owls' White Feathers Dazzle Prey Into Freezing Like A "Rabbit In Headlights"
Some barn owls use a remarkable and counter-intuitive method to catch their prey. By developing white feathers on their underside, these predators have lost the advantage of camouflage but gained something even better in return – the capacity to dazzle their prey for easier capture.
When confronted with bright light some nocturnal animals freeze like, well, a rabbit (or deer) caught in headlights. The number of roadside carcasses testifies to the drawbacks of this response, but cars are too new to have applied much selection pressure on these creatures. What is much more puzzling is the discovery, by Dr Luis San-Jose of the University of Lausanne, that owls have been making use of the same phenomenon, presumably for millions of years.
San-Jose was struck by the fact male barn owls come with two color schemes – one reddish-brown over the entire body, the other white feathers on the front. In theory, red owls should be able to successfully sneak up on prey that might be alerted to an approaching predator by a flash of white feathers, yet the white morph thrives.
In Nature Ecology and Evolution, San-Jose and co-authors describe a series of experiments that explain white barn owls’ success. Cameras placed in owl nests and GPS trackers on the owls themselves revealed that around the full Moon the reddish owls caught 43 percent less prey and their owlets often went hungry. Apparently any advantages the owls might gain from seeing their prey in moonlight were more than offset by the drawback of the prey being able to see them too. Female owls with red partners even time egg-laying so the owlets are not at their most vulnerable around full Moon.
Strangely, however, the white-bellied owls, which one would expect to be even more visible at full Moon, suffered no drop off in their hunting success.
To explain this paradox San-Jose put taxidermied owls on ziplines and “flew” them over voles, the barn owls' favorite prey. He found that voles “froze” for longer when they saw a white owl illuminated by light equivalent to a full Moon – five seconds longer than a reddish owl and almost 10 seconds longer than under new Moon conditions. Far from assisting escape, the extra warning voles got during this Moon phase left them more volnerable (sorry, not sorry) to capture, but only by the owls with white enough fronts to dazzle the voles.
The white owls caught slightly fewer prey during the duller new Moon and under cloudy skies, possibly explaining why not all barn owls are white, although the authors also suggest red owls benefit from daytime camouflage.
As Dr Jesús Avilés notes in an accompanying News and Views, what is puzzling here is why voles have not evoleved (still not sorry) to freeze less when they have been facing this monthly threat from above for eons.
