Unmasking Zorro: functional importance of the facial mask in the Masked Shrike (Lanius nubicus)

The facial mask is a prominent feature in the animal kingdom. We hypothesized that the facial mask of shrikes allows them to hunt into the sun, which accords them detection and surprise-attack capabilities. We conducted a field experiment to determine whether the mask facilitated foraging while facing into the sun. Male shrikes with white-painted masks hunted facing away from the sun more than birds with black-painted masks, which are the natural color, and more than individuals in the control group who were not painted. Furthermore, individuals with white-painted masks hunted at a greater angle in relation to the sun during the experiment than after the paint had eroded from the masks. Mean hunting success was significantly reduced in birds with white-painted masks compared with individuals with black-painted and natural masks. Moreover, individuals with white masks hunted with lower success during the experiment than in the following week when they reverted to their natural mask. We conclude that the facial mask of the Masked Shrike helps overcome the glare of the sun, perhaps allows better identification of prey from their larger shadow, and allows the shrike to approach the prey without alerting it to the stealth attack.