Bats originated approximately 50 million years ago. Although warm-blooded, many have "thermostats" that allow body temperature to vary with ambient temperature; they are therefore "heterothermic." There are 1300 living bat species -- about 20% of all mammal species. The Long-tongued Fruit bat has a wingspan of 1.5 centimeters; the Spectral Bat a wingspan of a meter. Many bats sport "noseleaves" --fleshy projections around the snout and nostrils -- which aid in the transmission of sound. DNA studies have determined that the closest living relatives of bats are not rodents but hoofed mammals and whales. There are twenty bat families, nineteen of which employ laryngeal echolocation -- the twentieth relies on tongue clicks -- as well as ten extinct families. Bats have five unique muscles: the occipitopollicaris connects the back of the head to the hand and runs along the anterior edge of the wing. The coracocutaneous anchors networks of elastic fibers to the armpit. The humeropatagialis tightens and braces the distal parts of the wing membrane. The tensor plagiopatii anchor the trailing edges of the wing. The depressor ossis syloformis controls the interfemoral membrane between the hind legs. Hoary Bats can fly at 27 kilometers per hour. Migrating Silver Haired Bats fly at over fifty kilometers per hour. The heart rate of an alert Little Brown Bat hanging in a roost at room temperature is about 200 beats per minute but while flying the heart rate increases to about 1000 beats per minute. The heart of a hibernating bat beats five times a minute. Flying bats consume energy at about twelve times the rate of resting bats. Bats can feel changes in air pressure with the skin of their wings. Some bats' feet lock into place when hanging upside down, so no energy is consumed except when the bat releases and drops. Common vampire bats engorged with blood have difficulty regaining flight. They urinate copiously, then use their long thumbs to provide extra lift leverage. Bats use echolocation (as do toothed whales, dolphins, shrews and tenrecs). When Lazzaro Spallanzani claimed (in 1794) that bats could see with their ears, he was widely mocked. "Does Signor Spallanzani also claim that bats can hear with their eyes?" Ultrasonic noises were not detected by scientists until 1938. Echolocation calls cover a range of frequencies. A Little Brown Bat searching for prey usually produces echolocations at the rate of twenty calls per second. but a Hoary Bat will produce only five calls per second. Calls increase in frequency during the actual attack. Bats can vary the length of the call from less than one millisecond to over 50 milliseconds. Bats are very loud to those who can hear them. A hunting bat can produce a sound that is twenty times more intense than the alarm of a smoke detector. Bats, unique among mammals, can turn off their hearing. At about two milliseconds before a vocalization is produced in the larynx, muscles in the middle ear contract, disarticulating three bones in the middle ear; then the ear is "reconnected" allowing it to hear the echo of the sound it has just emitted. Bats can be insectivorous, carnivorous, frugivorous, nectarivorous, piscivorous and sanguinovorous. Some bats eat birds, some eat other bats. Eastern Red Bats eat both tent caterpillars and gypsy moths. They must eat about 150 moths per night simply to retain their weight (thank you, Eastern Red Bats). The upper incisors of vampire bats are greatly enlarged, but since they don't chew their food, the cheek teeth are reduced to mere spicules. More than 500 species of flowering plants are pollinated by bats. Bats may eat up to 120% of their body weight each day. The common vampire bat can consume about two tablespoons of blood during a single night. Tiger Moths produce clicks that "jam" the echolocation patterns of bats. Because bats must minimize their weight, their digestive systems are extremely efficient -- Little Brown Bats move food through their system in twenty minutes. One million bats roost under the Congress Avenue Bridge in Austin, Texas. Bats are capable of eating 500 mosquitoes an hour. Some bats hibernate but bats can also enter into a state of torpor to consume less energy while roosting. Frio and Bracken caves in Texas each house over ten million Brazilian Free-tailed Bats during the summer. Bamboo bats roost in the hollow spaces in bamboo stems. In Borneo, Hardwicke's Wooly Bat roosts in the leaves of Raffle's Pitcher Plant and donates its feces to the plants nitrogen intake. Some Leaf-nosed bats bite the stems of banana and palm leaves in order to create tents for roosting. White-throated Round-Eared bats roost in excavated cavities of termite mounds. Hibernating Little Brown Bats bats breathe once an hour. Most bats bear one offspring rather than twins or multiples. Bats live surprisingly long lives. A banded Brandt's Myotis was at least forty-four years old. Vesper Bats mate in the fall but the female stores the sperm and does not ovulate until early spring. White nose disease is caused by a European strain of a common soil fungus. Bat droppings can contain spores that cause histoplasmosis in humans. Rabies, often bat-borne, kills 60,000 to 80,000 humans per year in Asia and Africa.
For more, see Bats: A World of Science and Mystery, by M. Brock Fenton and Nancy B. Simmons (Chicago: University Press, 2014).