When they lower their heads to graze, prey animals rotate their eyes to maintain horizontal pupils. “And by golly, when they pitch their heads down, the eyes rotate so the pupils stay parallel to the ground,” he says excitedly. And that’s a good thing because it means the animal is getting more light from what’s basically in front or behind it and less dazzling sunshine from above.īut what happens when grazers lower their heads to feed? Do their horizontal pupils become vertical? Can they still see panoramically? To find out, Banks spent several hours at the Oakland Zoo, photographing sheep and goats with their heads up and down. In a prey animal, a horizontal slit pupil gives the eye the most light from the sides and less from above. “They need to see clearly ahead of them, which is kind of out of the corner of their eye.” Like many other grazing prey animals, Barbary sheep have horizontal pupils and eyes on the side of their heads. “Now that’s an interesting problem, because their eyes aren’t facing the way they’re running,” Banks explains. Their eyes are also usually on the sides of their head: an adaptation to scan for predators in all directions.Īnd when they detect a predator, they run. That's why big cats like lions and tigers have round pupils, whereas smaller cats have slit pupils.Īnimals that are likely to be prey also tend to have slit pupils, but they are oriented horizontally. Taller animals can’t use that extra distance information from blur. And the blurry horizontal lines are also a distance cue themselves.īut Banks found that these benefits only hold for smaller animals that are closer to the ground. The ability to see sharper vertical lines improves the predator's ability to estimate distance. So the depth of field is also asymmetrical.įor cats, this means vertical lines behind the focal point stay relatively sharp, but horizontal lines at the same distance are completely blurry.Īnd that gives the hunters more precise cues to pinpoint their food. (Martin Banks)īut the aperture of a slit pupil is smaller in one direction than the other. The vertical lines of all three crosses are relatively sharp, whereas the horizontal lines of the two farther crosses are quite blurred. Three white crosses are placed at different distances from the camera, which is focused on the nearest cross. This image demonstrates how an image might look to an animal with an asymmetric depth of field. Photographers control depth of field by changing the size of the opening. The range that’s in focus is called depth of field. When a camera is focused on an object, things that are closer or farther away appear blurry. Turns out, vertical slit pupils are ideal for this job. Although domestic dogs have round pupils, smaller canine species like red foxes have vertical pupils. ![]() That means they need to estimate the distance to their food accurately. These predators hide patiently, and then strike suddenly. And like cats, the vast majority of ambush hunters also have vertical pupils. Instead, they hunt by stealth.Cats are ambush predators. Their small size means they cannot chase prey actively like the big cats. Conversely, The small cats had vertical slit pupils because they were more likely ambush predators. The researchers discovered that taller animals that chase prey, such as lions, tigers, and wolves, tend to have round pupils. Based on this research, the main reason the eyes of lions don’t look like that of small cats is their place in the ecosystem. The scientists correlated these animals’ eye shapes (round, horizontal, and vertical) to their lifestyle in terms of how they forage for food and the time of the day they were more active. For the study, Banks and his colleagues analyzed 214 land animals. The study, carried out in collaboration with Durham University in the United Kingdom and published in the Science Advances journal, presents a hypothesis that links eye shape to the ecological niche occupied by an animal. Martin Banks, a professor of optometry at UC Berkeley, conducted extensive research on this subject to answer the question of the difference in eye shape in different animals. They hunt prey differently and are more active during the day than at night. Basically, lion eyes don’t look like cat eyes because they are bigger. No one knows for sure why this is so, but scientists have put forward a persuasive theory to explain the differences in the eyes of both felines. ![]() ![]() Unlike cats with vertical slits, lions have round pupils.
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