Table 1.
Axial diameter (AD) of eyes used in generating species-specific contrast sensitivity functions, together with visual acuity estimates (cpd) of the four mammalian species of interest under different illumination conditions.
Also shown is the corresponding minimum resolvable visual angle subtended on the retina by the target of interest. AD values for zebra and human (in parentheses) are provided for context, and were not used to estimate acuity.
Fig 1.
Photographs of a (a) plains, (b) mountain, and (c) Grevy’s zebra, and (d) African wild ass in the Tierpark Zoo, Berlin.
All photos by Tim Caro.
Table 2.
Estimated maximum distance at which zebra stripes can be resolved by different species of viewers, by body region.
Fig 2.
Image of a solitary plains zebra at a distance of 6.4 m as it may appear to a human, zebra, lion and spotted hyaena under photopic conditions.
As shown, stripes are detectable to all species at this distance.
Fig 3.
A small group of plains zebra taken at a real-world equivalent of 16.4 m as they may appear to a human (a,c,e) and lion (b,d,f) under photopic (bright; daylight), mesopic (dim; dusk) and scotopic (dark; moonless night) conditions.
Stripe visibility falls off from human vision to lion vision and as ambient light decreases.
Fig 4.
Groups of zebra (a,b), zebra and topi together (c,d), waterbuck (e,f), and impala (g,h) on the Katavi plains from a real-world viewing distance of 9 m.
Images are scaled such that size variation between species reflects true differences among species. Images are modeled for human (left panels) and lion (right panels) visual systems under photopic conditions.
Fig 5.
A solitary zebra on the plains (a), and on the outskirts of a forest (b), as well as striped (c) and uniformly grey (d) models of zebras in the woodlands.
Images are modeled for a lion visual system under photopic conditions.