A STRIPE FOR ANY OTHER PURPOSE?

Uncovering the adaptive complexities of falcons' malar stripes

- MICHELLE VRETTOS, CHEVONNE REYNOLDS & ARJUN AMAR

Falcons are easily recognisable by their dark malar or moustachial stripes. Ornithologists have often speculated about the evolutionary significance of these stripes, and one prominent hypothesis has suggested they might help mitigate the effects of glare when the birds are hunting. According to this 'solar glare hypothesis', the dark feathers below the falcon's eyes absorb sunlight, preventing it from being reflected into the eyes and thus improving the bird’s ability to hunt in bright conditions.

In 2021, Fitz researchers provided the first empirical data supporting this hypothesis. We investigated the relationships between climatic variables and geographic variation in the malar stripes of Peregrine Falcons using 2197 photographs provided by citizen scientists across the species' range. Peregrines inhabiting regions of higher solar radiation had wider and darker malar stripes, which suggests that the hypothesis is well founded.