Are bats really blind?

Bats are not blind. Every bat species has functional eyes and can see, although how well they see differs from one species to the next. The phrase "blind as a bat" is a myth. The U.S. Geological Survey describes bats as having small eyes with very sensitive vision, which lets them see in conditions humans would consider pitch black, though without the sharp, colorful vision humans have. [1] [2] [3]

Researchers measure sharpness of vision in cycles per degree, where a higher number means finer detail. Human acuity is between 45 and 60 cycles per degree depending on the light. The rufous horseshoe bat, an insect eater with small eyes, has an estimated acuity of 0.35. Larger-eyed bats, such as the Australian ghost bat and the fruit-eating Indian flying fox, can resolve detail at around two cycles per degree. So bats see far less detail than people, but they do see. [1]

The Bat Conservation Trust notes that flying foxes have great night vision, while bat species in the UK do not have very good night vision, a bit like humans, and rely more on echolocation. [4]

Bat eyes are dominated by rod cells, which work in dim light, and up to two percent of their photoreceptors are cones. Genetic studies suggest that all bats studied so far can sense orange and red wavelengths, which suit low light. Some, such as the greater horseshoe bat and the white-winged vampire bat, have lost the ability to tell blues and violets apart. [1]

Some bats may perceive light that humans cannot. At least seven insect-eating species have shown behavioral responses to ultraviolet light, and the nectar-feeding Pallas's long-tongued bat can discriminate colors down to about 310 nanometers. [1]

Most bats navigate in darkness by sending out ultrasonic sounds and listening to the echoes, which builds an acoustic picture of their surroundings. Bats can detect objects as thin as a human hair this way, and can find insects the size of mosquitoes. [5] [6]

Echolocation does not replace sight. A 2022 commentary in Current Biology describes a study in which wild Egyptian fruit bats, which have prominent eyes, kept echolocating with tongue clicks in broad daylight and raised their click rate near obstacles, just as they do at night. The author concludes that bats use both senses, especially as tasks become more complex. In bats that produce sonar with the larynx, vision is generally treated as a secondary sense, yet combining sight and sound can still help them. [5]