Perceiving zebra rump stripes “through the eyes of” their predators: A study with human observers

Which particular selective pressures guided the evolution of zebra stripes? This question, one of biology's most celebrated conundrums, is also of potential interest to readers of Perception, as, on most accounts, stripes’ benefits to zebras reflect perception of stripes by their predators, parasites, or conspecifics. Although stripes do not seem to camouflage zebras or warn off predators, various accounts implicate perception, including proposals that stripes disrupt predator perception, aid intra-species recognition, or deter biting flies. Currently, only the last of these enjoys strong empirical support: narrow stripes on zebras’ heads, necks, shoulders, limbs, and flanks are known to deter biting flies, and variation in patterns of those stripes is associated with parasite burden, not predators, across species. Rump stripes, however, are different. Typically broad and horizontal, there is some evidence that they vary with hyaena threat rather than parasites, consistent with an antipredator role. Here, viewing images of zebras, filtered to simulate lion and spotted-hyaena vision at distance or in motion, human observers typically judged rump stripes to be the most attention-capturing regions of the images. Computational models implicated visual salience in this effect, and pursuit simulations showed that by driving predators’ attention to a zebra's rear, rump stripes could minimise the probability of capture.