Cats aren’t nocturnal.
Everyone with a cat knows that felines love running around at night, especially when their so-called owners are trying to sleep. Despite that, cats aren’t actually nocturnal — they’re crepuscular, meaning they’re most active during dusk and dawn. The reason they prefer twilight has to do with their hunting instincts, as their eyes are well attuned to low-light conditions that allow them to see their prey while remaining hidden themselves. And because they’re descended from desert hunters, dusk and dawn are also favorable due to cooler temperatures. This doesn’t stop them from sleeping all day, of course, but they’re always ready to wake up in an instant — an adaptation that helps keep them safe from predators and alert to opportunities for tiny prey.
Cats are hardly the only crepuscular creatures. Deer, rabbits, bears, skunks, and possums are among the other mammals you can see out and about as the sun is rising or setting. Birds such as barn owls and common nighthawks can also be crepuscular. Animals you might be surprised to learn are mostly nocturnal include koalas, beavers, and scorpions, among others — and some of them exhibit a level of nighttime activity that could even tire out your cat (maybe).
It’s called the tapetum lucidum (Latin for “shining layer”) and it works like a small mirror to reflect light, helping cats see in the murk — another evolutionary adaptation that partially explains why your feline is so wired while you’re snoozing. Cat eyes are special in other ways, too. Their pupils grow up to 50% larger in dim light than ours do, allowing them to see more clearly, and they have more light-sensing rods in the back of their eyes. Dogs, cattle, deer, ferrets, and horses have the tapetum lucidum as well, but their eyes don’t all glow the same color as each other. The hue has to do with the amount of pigment in their retina, as well as other substances in the tapetum, meaning that even two dogs of the same species might have eyes that reflect a different color.
