Are bats blind?
Just how blind are you if someone claims you’re as blind as a bat? This isn’t an easy question to answer. You’d better start by asking your accuser to be more specific.
There are hundreds of species of bat. Some eat insects, others fruit, still others go for small animals, or birds, or nectar, or blood. Some roost in trees, others in caves. Each species makes use of a number of senses, including vision. Bats don’t all see the world the same way but they can all see.
The blindness of bats is an old assumption, one that was bolstered by the discovery last century that bats use echolocation — sonar — to get about in the dark. Just because bats have this incredible sense based on sound, though, doesn’t mean that they are blind. You may as well argue that dogs are blind by dint of their superlative noses.
Most bats echolocate. But not all of them. And echolocation has its downsides, too. It uses a lot of energy, it only works over a short range and it doesn’t work well in a cluttered environment. Almost all bats are nocturnal so their eyes are adapted to the dark and to filling the gap beyond the range of echolocation.
It seems that in the dark most bats don’t rely as much on vision as we do, preferring echolocation, regular hearing and smell, but there is nothing wrong with their eyesight. What little research there is on bat vision suggests that when the light is good bats will make use of visual cues, and sometimes even require them. Like birds, bats sometimes fly into windows which indicates that vision is important for navigation and sometimes trumps echolocation. At least one kind of bat can even see into the ultraviolet, a trick I’d like to see you try.
Far from being the sensory equivalent of the appendix, a bat’s eyes are sensitive and useful. Just as we are reluctant to rely solely on our ears, bats seem reluctant to rely on their eyes alone. But blind? That’s just plain batty.