Mammals
Bat
Chiroptera · also called bats
A bat is a mammal that solved flight and then solved darkness. Its wing is a sheet of skin stretched over a hand of enormously long fingers, and most bats find their way and catch their food not by sight but by shouting into the night and reading the echoes. One in every five mammal species is a bat.
Overview
Bats are the order Chiroptera, around 1,470 species, roughly a fifth of all mammals, on every continent except Antarctica. A bat is the only mammal that truly flies, flapping a membrane wing stretched over elongated finger bones. Most bats eat insects; the fruit bats eat fruit and nectar and are major pollinators; a few take fish, frogs, or, in three species, blood.
Hunting in the dark
Most bats echolocate, sending out ultrasonic calls and building a detailed sound-picture from the echoes, fine enough to catch a mosquito or pluck a spider from its web in total darkness. Bats roost by day in caves, trees, and buildings, and Bracken Cave in Texas holds 15 to 20 million — the largest gathering of mammals on Earth.
Vital, and in trouble
Bats eat vast numbers of crop pests and pollinate hundreds of plants. But white-nose syndrome, a fungus found in North America in 2006, has killed millions of hibernating bats, and wind turbines, roost loss, and deforestation add to the pressure.
Status
Bats as an order are Not Evaluated, but about a fifth of species are threatened or too poorly known to judge, and modern threats are mounting.
Bat: common questions
How does echolocation work?
An echolocating bat sends out a stream of very short, high-pitched calls, usually through the mouth but in some species the nose, and listens for the echoes bouncing back off objects around it. From the time an echo takes to return, the bat judges distance; from the difference between the two ears, direction; and from subtle changes in the echo's pitch and pattern, it can tell the size, shape, texture, and even the wingbeat of a flying insect. As it closes on prey, the bat speeds up its calls into a rapid buzz for a precise final fix. The whole system is fast and detailed enough for a bat to hunt small moving insects in complete darkness and to fly through cluttered forest at speed.
Are all bats blind?
No, and the phrase blind as a bat is wrong. Every bat has functioning eyes, and the large fruit bats, or flying foxes, have big eyes and good vision and use sight, not echolocation, to find their food and roosts. Even the small echolocating bats can see, and some use vision alongside sound, for example to detect the glow of the horizon at dusk or to spot a familiar landmark. Echolocation is an addition that lets bats operate in darkness, not a replacement for eyes. In good light many bats will use vision, and in the lab bats can be trained on visual tasks.
Do vampire bats really drink blood, and are they dangerous?
Yes, but only three of the roughly 1,470 bat species do, and all three live in Latin America. A vampire bat lands near a sleeping animal, usually livestock, makes a small painless cut with razor-sharp teeth, and laps the blood that flows, helped by an anticoagulant in its saliva. It takes a tablespoon or so and the host rarely notices. Bites on people are uncommon and the direct blood loss is trivial. The real concern is rabies, which vampire bats can carry and transmit, causing livestock losses and occasional human deaths in rural areas, which is why vampire bat control and rabies vaccination programmes exist. The anticoagulant, nicknamed draculin, is being studied as a drug to treat stroke.
Why do bats matter, and why are they declining?
Bats are keystone animals in many ecosystems. Insect-eating bats consume enormous quantities of moths, beetles, and mosquitoes, and studies estimate they save farmers billions of dollars a year in avoided pest damage and pesticide use. Fruit and nectar bats pollinate and disperse the seeds of a huge range of tropical plants, including many of commercial value, and are essential to regenerating cleared forest. Yet bat populations are falling. White-nose syndrome has devastated hibernating bats in North America, wind turbines kill large numbers of migrating bats, roosts in caves, mines, and old buildings are lost or disturbed, tropical forest is cleared, and bats are still killed out of fear and misinformation. Because most bats breed slowly, raising one pup a year, recovery from any of these is slow.