The common saying “blind as a bat” suggests these flying mammals cannot see, but this widespread belief is entirely false. Bats possess functional eyes and rely on vision as an important part of their sensory world. Their ability to navigate in the dark is an evolutionary advantage that allows them to thrive in the nocturnal niche. A bat’s sensory system is a sophisticated combination of sight and sound, each serving a distinct purpose.
Dispelling the Myth: Bats Are Not Blind
The misconception of bat blindness likely arose from their strictly nocturnal habits and the discovery of echolocation, their remarkable sonar system. Since they hunt and fly where human vision is ineffective, it was mistakenly assumed that sight played no part in their survival. All of the over 1,400 bat species possess eyes, and none are truly blind.
Many bats have sharp eyesight, especially those in the suborder Megachiroptera, often called fruit bats or flying foxes. These bats typically have large eyes and depend on sight for finding food and navigating, with some species having vision three times better than humans in low light. Even the smaller microbats, which rely heavily on echolocation, use their eyes for long-distance navigation and detecting predators.
The Mechanics of Bat Vision
Bat eyes are highly specialized organs optimized for detecting movement and contrast in low-light environments. Their retinas contain a high concentration of rod photoreceptor cells, which are responsible for vision in dim light and are far more sensitive than cone cells used for color vision. This adaptation allows them to maximize the collection of scarce photons after sunset.
Research shows that many bat species, including some microbats, possess two types of cone opsins, giving them the prerequisite for dichromatic color vision. Some bats, like the nectar-feeding Glossophaga soricina, can see into the ultraviolet (UV) spectrum. This UV sensitivity helps them locate flowers that reflect UV light or identify landmarks during dusk and dawn. Their lenses and corneas are also highly transmissive to UV light, unlike most other mammals whose eyes filter out this radiation.
Vision and Echolocation: A Dual Sensory System
The bat’s sensory world is defined by the complementary roles of vision and echolocation. Echolocation, which involves emitting ultrasonic pulses and interpreting the returning echoes, is effective for short-range tasks. It allows for the precise detection and tracking of small, moving objects, such as insects, even in complete darkness. For small prey, the detection range of echolocation is superior to that of vision.
Vision is the superior tool for long-distance orientation and detecting large, stationary objects like cliffs or trees. Echolocation’s effective range is typically limited to tens of meters, requiring bats to use their eyes for navigating long distances between their roost and foraging areas. Megabats, which primarily feed on fruit and nectar, rely heavily on sight to spot food sources and navigate broad landscapes. Microbats use sight to monitor the general environment, spot distant landmarks, and orient themselves against the horizon, integrating both streams of information.