Like humans, cats rely on the five senses of vision, hearing, smell, taste, and touch to tell them about the surrounding world. These senses gather information and send it, via nerves, to the brain for interpretation. Cat senses evolved over millions of years to suit their pre-domesticated way of life: that of a nocturnal hunter with exemplary night vision and extraordinary senses of hearing and smell.
Cats have very large eyes that work most effectively at night, when mice, a main source of prey, are most active. Rods— photoreceptors responsible for black-and-white vision in dim light—outnumber cones (responsible for color vision) in the cat’s retina by 25:1 (in humans the ratio is 4:1). Cats do have color vision, but it is not as important to them as their night vision. They can see blues and yellows, but reds and greens probably appear as grays. In daylight, the pupils shrink to vertical slits to protect the eyes from glare.
Cat vision is much less sharp than that of humans. Focusing such large eyes takes effort and cats are generally farsighted, unable to see clearly within about 1ft (30cm) of their eyes.
Their vision is much more attuned to detecting movement. Like many other predators, cats have forward facing eyes. Their total field of vision is about 200º, with an overlap between the eyes of 140º. This overlap gives the cat binocular vision, allowing it to see in depth and to judge distances accurately, which are essential for success when hunting.
Cats have superb hearing, with a range that extends from 40 to 65,000 Hertz. That is two octaves higher than humans can hear (up to 20,000 hertz) and into the ultrasound region. This wide range covers all the sounds important to cats, including the vocalizations of other cats and enemies, and the rustling of rodents and their high-pitched squeaks. Cats can independently swivel the external parts of the ear, the pinnae, up to 180º to pinpoint the source of a sound.
The pinna’s design also allows cats to determine the height from which a sound emanates, which is very useful for an animal that climbs. The inner ear contains the vestibular apparatus, or the organ of balance. It registers changes in direction and speed and allows a cat to right itself when falling (see pp. 54–55). Cats also use their ears to communicate their mood: for example, rotating the ears back and flattening them indicates anger or fright. Cats are extremely sensitive to loudness, about 10 times more so than humans. That is why they dislike noisy environments and become agitated by disturbances such as fireworks.
SMELL AND TASTE
Cats have a powerful sense of smell, not as strong as a dog’s but much more acute than a human’s. The sensory membrane inside the nasal passages where smells are trapped is five times bigger than the same region in humans. Cats recognize each other by smell and use it to help track prey. They also employ scents from urine, feces, or glands to mark their territory, warning other cats to keep away or advertising their sexual status. The smell is closely linked to taste. A cat will usually smell its food—to check that it is edible—before eating. Taste buds on the upper surface of the tongue mostly respond to bitter, acidic, and salty chemicals in food. Cats can also recognize sweet tastes, but as strict carnivores, they have little need for sugar.
Cats have a sensory organ in the roof of the mouth called the vomeronasal, or Jacobson’s, organ. Using this, a cat produces an open-mouthed grimace—“flehman response”—as it laps up scents, usually those of a sexual nature left by other cats.
The hairless parts of a cat’s body—the nose, paw pads, and tongue—are highly sensitive to touch, as are the whiskers. Technically known as vibrissae, whiskers are deeply embedded modified hairs. The most prominent whiskers are on the sides of the nose. Smaller whiskers are on the cheeks, above the eyes, and on the back of the forelegs. Whiskers help cats navigate in the dark and also to “see” nearby objects that the eyes cannot focus on. The whiskers on the head also help to judge the width of gaps through which their body can pass.