![]() So, the next time you find yourself face to face with a cat, remember this: it knows exactly how far away you are.Predator-prey interactions play a key life history role, as animals cope with changing predation risk and opportunities to hunt prey. Vertically oriented pupils may give ambush predators an edge on pouncing their prey. “The most interesting cases, of course, are the counter examples that don’t fit the pattern,” he says. It’s an ambush predator, but it has horizontal slit pupils. He would also like to see more discussion of the animals that buck the trends. Heesy suggested that analyzing mammals separately and including a wider range of species like rodents, primates and marsupials would give a stronger test of the authors’ theories. “It’s a fun study,” says Chris Heesy, a professor of anatomy at Midwestern University in Arizona. And the eyes have to rotate in different directions - one clockwise, the other counterclockwise. ![]() In fact, sheep can rotate their eyes up to 50 degrees to maintain horizontal pupils. 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.
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