Why do animals have different pupils?

The right eyes for the job are a matter of life and death

The pupil is the opening in the eye’s iris that lets in light. It appears black because the eye tissue absorbs light, and it changes size as the iris dilates and contracts to adjust the amount of light that enters the eye.

Many animal species have eyes, but they don’t all have the same pupils. In a recent study, scientists concluded that different pupil shapes perform different jobs.

Round pupils

Animals like dogs, wolves and big cats have round pupils. They actively chase down prey, mostly in daylight. Round pupils mean that the field of view isn’t spectacularly wide, but as top predators their vision isn’t required to help them flee from attack.

 

Vertical slit pupils

The animals that sport these pupils
are small ambush predators that hunt close to the ground: cats, foxes and even crocodiles. The slits allow a greater expansion of the pupil to let in much more light — an adaptation to predators hunting in a variety of light conditions.

 

Horizontal pupils

Horizontal, oblong-shaped pupils are a feature of prey animals like sheep, goats and horses. These curious-looking pupils provide a wide field of view, allowing the animals to scan for potential predators. The pupils also keep the ground in sharp focus to aid escape.

 

Horizontal slit pupils

These pupils are also a feature of prey- like animals, seen in some frogs, toads, snakes and octopuses. This pupil type allows the animal to spot the vertical motion of predators and therefore take evasive action. They also extend wide to let plenty of light in for day and night foraging.

 

For even more eyes and answers to your animal questions, pick up a copy of issue 51 of World of Animals, in shops or online!