By Ben Berejka ’20
When picturing nocturnal predators, most people would envision darkly colored and cryptic monsters creeping through the shadows, but a recent study published in Nature Ecology and Evolution describes the opposite. Researchers observed that whiter and brighter barn owls are, surprisingly, more successful hunters than their orange and brown conspecifics. While the whiter colored owls stand out more to prey it seems that those owls utilize the advantage of surprise when they encounter unsuspecting prey [1].
Barn owls are one of the widest ranging species of owl and can be found across several continents. They can generally be found in two different color morphs: owls with white underbellies and faces, with an orange/brown and peppered backside, or owls that are orange all over and peppered across the back. Researchers observed that under moonless nights neither color morph had any greater success than the other, averaging roughly 5 prey catches across the night. However on nights illuminated by the moon the success of orange morphs decreased, while the whiter morphs and brighter white morphs remained as successful or even more successful than moonless nights [2].
To test these observations researchers designed an experiment asking how the brighter owls managed to maintain their success. They placed captive voles inside of a terrarium at the base of a zipline. At the top of the zipline was a black curtain concealing either a white morph or orange morph taxidermy barn owl. The room was kept dark besides a halogen light used as a proxy for the moon (Fig. 1). After the voles were exposed to the owls researchers recorded that voles remained startled for up to five seconds longer when the whiter owl was sent down the zipline. They proposed that brighter owls may have been naturally selected to take advantage of the voles’ aversiveness towards light and that this lightness gave more reflective owls a greater element of surprise over their prey.
You may be wondering then why all barn owls are not the brighter white morph color. Why does the orange color persist? The researchers describe and predict that the orange coloration may still be advantageous for camouflage in the nest. Additionally, male owls are usually brighter and whiter than the females and do more of the hunting while chicks are present in the nest. This suggests that the brighter color may not only help hunters, but also could be used as a signal of mate fitness. This study has not only helped to better understand barn owls, but to illuminate potential areas of research in nocturnal predator coloration.
[1] San-Jose LM, Séchaud R, Schalcher K, Judes C, Questiaux A, Oliveira-Xavier A, Gémard C, Almasi B, Béziers P, Kelber A, Amar A. Differential fitness effects of moonlight on plumage colour morphs in barn owls. Nature ecology & evolution. 2019 Sep 2:1-0.
[2] Gorman, James. “White Barn Owls Thrive When Hunting in Bright Moonlight.” The New York Times, The New York Times, 2 Sept. 2019, www.nytimes.com/2019/09/02/science/moon-owls-voles.html?searchResultPosition=28.
