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Up close of a lion's eye
A lion’s pupils are round, unlike those of a domestic cat © Simon Vegter
SPONSORED CONTENT written by Dianne Kokkonidis, Wild Wings Safaris

Have you ever wondered why lion’s eyes have round pupils and not vertical slits like your pet cat? This was one of the questions a team of researchers at the University of California in Berkeley set out to answer in a 2015 study. When they looked at the pupils of 214 species of land animals and controlled for their ecological niche, results showed that species with vertical slit-shaped pupils tend to be ambush predators that hunt in both daylight and at night. They concluded that the shape of an animal’s pupils is usually linked to how it hunts.

Predators with vertical slit-shaped pupils tend to ambush their prey. Predators with circular pupils generally chase their prey down as “active foragers”.

African wildcat
The African wildcat, like the domestic cat, has vertically slit pupils to aid in the ambushing of its prey © Simon Vegter

Your pet cat’s pupils give it the dynamic range it needs to hunt in the dark without being blinded by the sun during the day. Yet the same could be said about the needs of the big cats as almost all big cat species are ambush predators to a certain extent. Why then do the larger cats have round pupils instead of slits?

The answer lies in height difference…

Cheetah in the wild
The cheetah’s dark eyes also help to reduce glare © Simon Vegter

Vertical slit-shaped pupils are not only associated with how a predator hunts but also how small the predator is. The study found that 82% of the 65 ambush predators with forward-facing eyes measured less than 42 centimetres from ground to shoulder height.

“So domestic cats have vertical slits,” postdoctoral co-author of the study, William Sprague, elaborated, “but bigger cats, like tigers and lions, don’t. Their pupils are round, like humans and dogs”.

The difference in pupil shape comes from the way in which smaller animals use focus blur in order to gauge distance more effectively than taller animals.

Africa Geographic Travel
Painted wolf, African wild dog
Painted wolves (African wild dogs) are “active foragers”. Their pupils are, therefore, round © Simon Vegter

And animals with horizontal slit-shaped pupils like antelope, zebra and buffalo? Horizontal slit-shaped pupils appear to be a feature of prey animals who graze. Using computer models, the Berkeley researchers were able to establish that horizontal pupils allow prey species to align their vision with the ground which permits more light to enter their eyes from the front, sides and back.

Zebra's eye
Horizontal-slit pupils allow zebra to detect potential threats while grazing © Simon Vegter

This is important because, according to the lead author of the study, Martin Banks, a panoramic visual ability with minimal blind spots is critical for these animals. They need to be able to spot predators that approach from the ground and “once they do detect a predator, they need to see where they are running. They have to see well enough out of the corner of their eye to run quickly and jump over things”.

Up close of buffalo, buffalo's eye
Although dangerous when provoked, buffalo are not predatorial. They are grazers © Nicky Firer

Next up, the team of researchers are hoping to leave terra firma. Looking to the skies and going underwater, they want to see what they can discover about the pupils of the animals that call air and water their home.

If you want to know more about this study you can read it here: Why do animal eyes have pupils of different shapes?

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