BATS
Bats are the world's only flying mammal (flying squirrels glide). They are the dominant flying creatures of the night while birds are the dominant flying creatures of the day. Bats are found everywhere on the earth's surface except a few isolated islands, the polar regions and the most inhospitable deserts. Most of the billions of individual bats are found in the tropics. [Sources: Merlin Tuttle, National Geographic, April 1986;Alvin Novick M.D., National Geographic, May 1973]
Bats evolved from insect-eating mammals and are closer relatives to primates than they are to rodents. Their closest relatives are shrews. The oldest bat fossils date to 50 million years ago, compared to 140 million years ago for birds. Bats from this time period are not all that different from modern bats.
It believed the mammals that evolved into bats were shrew-like insect eaters that pursued their prey up trees and began my making leaps to catch insects and evolved a mechanism to glide and eventually grew elongated fingers shortened its arms and grew skin from its legs to elongated fingers, producing wings. A 50-million -year-old bat fossil found in Wyoming had traces of insects in its stomach and elongated fingers and impressions of wing membranes similar to those of modern bats.
Bats are the second largest group of mammals with 1,100 species (rodents are the largest group, with 2,020 species). They make up nearly a quarter of all mammal species, and vary in size from the tiny bumble bat of Thailand, which weighs less than a moth, to flying fox in Indonesia with a wingspan of 1.8 meters.
Websites and Resources on Animals: ARKive arkive.org Animal Info animalinfo.org ; Animal Picture Archives (do a Search for the Animal Species You Want) animalpicturesarchive ; BBC Animals Finder bbc.co.uk/nature/animals ; Animal Diversity Web animaldiversity.ummz.umich.edu ; International Field Guides media.library.uiuc.edu ; animals.com animals.com/tags/animals-z ; Encyclopedia of Life eol.org ; World Wildlife Fund (WWF) worldwildlife.org ; National Geographic National Geographic ; Animal Planet animal.discovery.com ; Wikipedia article on Animals Wikipedia ; Animals.com animals.com ; Endangered Animals iucnredlist.org ; Endangered Species Resource List ucblibraries.colorado.edu ; Biodiversity Heritage Library biodiversitylibrary.org
Websites and Resources: Bat Conservation Trust bats.org.uk ; Bat Conservation International batcon.org ; Wikipedia article Wikipedia ;
Merlin Tuttle, the founder and president of Bat Conservation International.
Bat Characteristics and Behavior
The bodies of bats have a number of modification like those on birds that aid flight, namely light weight bones that resemble straws.
In temperate climates bats hibernate in winter. Places where large numbers hibernate — caves, abandoned mines and the like — are known as hibernaculums.
Most bats are nocturnal. They generally emerge at dusk, gorge on insects or fruit during the night and hang upside-down when they sleep during the day. Those that feed on insects help to get rid of pests such as mosquitos and crop-destroying bugs. Those that eat fruit or feed on nectar or pollen play as important a role in plant reproduction as birds and bees. Their image as carriers of evil and suckers of blood have led to their extermination, which is unfortunate because they are arguably more helpful to mankind than any other wild animal.
Bat Wings
Bats are excellent fliers. They can snatch insects out of the air and hoover in front of flowers and reach heights of 10,000 feet. Since they hang upside down they have no trouble launching themselves into the air, they simply fall and start flapping. Many bats are incapable of walking or taking off should they ever land on their feet.
Bats developed wings by modifying their forearms and hands. Their bony, elongated "fingers" are the superstructure for their wings, supporting the elastic membranes of the wings like the ribs on an umbrella. The membranes themselves are sometimes so thin you can see right through them. A bat’ss thumb is not attached to the wing membranes. It serves as a hook that allows the bat to climb around on its roost.
Bats wings are quite different from the wings on airplanes and birds. They are quite stretchy and change their shape with every stroke. Some bats have a braking device that acts like a parachute on a drag racer. It stays retracted when the bat's legs are together and opens up when the bat spreads its legs apart, slowing the bat down. Bats are also aided in flight by their thin, flexible bones. The primary support of their wings is the fingers on their hands. This allows for full movement of the shoulder joints allowing the wings to flap.
Bat Flight
Bats take off land upside down, with females often do this with having young clinging to them. Taking off isn’t that hard: they just drop off and start flapping. Some bigger species have to beat three or four times to lift their bodies from a vertical position. But landing requires great skill, sort of like a figure skater doing a triple axel on the ceiling rather than the floor.
Daniel Riskin, a biologist at Brown University, has studied how bats land and found they perform a flip and sometimes a twist before making a four point or two point landing. Using a high-speed video camera to observe two cave-dwelling species and one tree-roosting species land he found that the tree-roosting bats made hard landings on all four limbs while cave-dwelling ones turned slightly during their flip to land on their hind legs only.
The flight mechanics for bats is quite different than that of birds. In the slow flight of birds, for example, the downstroke of the wings occurs with the feathers compressed to produce lift. On the upstroke the feathers separate to allow air to pass through so the wing can return to the upper wing position with a minimum of interference to flight. A bat can not do this because its wings are a membrane that offers continuous resistance.
Studying Pallas’s long-tongued bats in a wind tunnel, Anders Hedenstrom of Lund University in Sweden found that both the downstroke and upstroke push the bat up and forward, Stephan Reebs wrote in Natural History magazine: “To move the bat forward and up during the upstroke, the outer part of the wins flips upside down and flicks quickly backward. (At high speeds the wing doesn’t flip and part of it does push the bat down during the upstroke, but that resistance is at least partly compensated for by continuous lift on the front of the wing at higher speed).
Bat Senses
All bats have eyes and can see. Many kinds of bats don’t see very well and rely on echolocation (See Below). Some have extraordinary night vision. Fruit species in particular have very sensitive eyes, which they use for navigating instead of echolocation. Even though they see well at night they need a little light and thus can not see in the complete darkness of caves, which is one reason why they roost in trees rather caves. .
Many bats have huge ears. Some are reminiscent of those belong to gremlins in the movie “Gremlins” The ears of some species are so large they coil up like a party favors when they sleep so they don’t disturb their roosting neighbors.
Bats can sense it is dark and time to leave a cave even though they can not see it get dark and can not sense the cooling temperatures of approaching night because the temperatures in the cave are relatively stable throughout the day.
Bats also have an excellent sense of smell. They can sometimes detect food sources a mile or more away. The male hammerhead bat has a snout so big in relation to the rest of its body it looks like a mouse-size hippopotamus with wings.
Bat Echolocation
Most bats navigate their way through forests and open spaces, and locate prey and avoid predators, using echolocation — a biological sense based on the same principal as radar. Bats send out signals that bounce back and are detected and analyzed, giving bats a detailed picture of objects struck by the signals and their distance from the bat.
In bat echolocation ultra-high frequency pulses emitted 10 times a second sounds are emitted from the bats mouth (sometimes through a labyrinth of lips that direct of the sound in different direction) and are detected with the bat’s ears of with ear-like organs comprised of folds and flaps that are located on the face of the bat and act like radar dishes.
Bats decode information that bounces back. The time delay and angle provides information about distance, location, movement, the composition of an objects, and possibly even altitude measurements, allowing the bats to zero in on the targets and avoid obstacles or threats.
Echolocation is used primarily by small insect-eating bats, whose eyes have become so small they are of little use. Leaf-nosed bats have a leaf-shaped nose, which is used for vocalization rather than their mouths. It both modulates and focuses the sound. Echos are picked up with the ears.
Bat Sounds
A flying bat using echolocation uses sound between 50,000 and 200,000 vibrations a second. Most human-heard sound are several hundred vibration per second with some people, mostly children, able to hear sounds with 20,000 vibrations a second. Very high sounds are also the basis of sonar used by submarines and ships to detect objects in water. The effect is similar to radar but radar uses radio waves whereas sonar and bat echolocation use sound waves.
David Attenborough wrote: “It is reasonable to guess that the shrew-like ancestors of these bats used high-pitched sounds to find their way in the dark, just as living shrews do today. It is no surprise therefore that their descendants still do the same. What is surprising — indeed astonishing — is the way in which bats have elaborated those simple ultrasonic squeaks into the superb navigational and hunting system they use today.”
Bats generate sound with the larynx in their throat and direct it through both their nose and mouth and pick up sound with their highly sensitive ears that it many cases can be twisted to detect sound and are translucent, ribbed with cartilage and laced with blood vessels. Bats swing their head rapidly from side to side, sending out sound and picking up echos, and deducing information from those echos, as they fly at speeds of up to 40 mph.
Bats send out sound in short bursts, 20 to 30 times a second. Most bats wait to receive the echo of one signal before emitting the next. The closer the bat is to an object the shorter the time taken for the echo to come back, so they can increase their accuracy as its closes in for the kill. When it eating it so momentarily blind as it can not send out sound in a normal way with food in its mouth. Some species avoid this problem by squeaking through their noses and have developed unique megaphone-like structures to achieve this end.
Attenborough wrote: “Many bats focus the sound beam using a structure called a nose lead that surrounds the nostrils. This varies widely in shape from species to species. There are bowls, slits, leaves, vertical spears, horseshoe-shaped cups and shapes that are so complex and convoluted that they can not be compared with any simple object. Many are mobile in that their owners can vary the width and character of the beam they project. The sound themselves are emitted as a series of extremely short stabs, They are so high-pitched they are far beyond the range of our own ears. But they are extremely powerful. If we were able to transport them down at their true voice they would sound as loud to us as a jet engine.”
Bat Echolocation Vibrations
The bat echolocation system is so sensitive that bats can detect the footsteps of insects, the scales on moths, the difference between a rock and a beetle, the difference between flowers and other plants and make out a wire as thin as a human hair suspended across its flight path. Many bats can fly fine if they are blindfolded but start crashing and bumping into objects if their ears are plugged and their echolocation system is messed up.
People can hear squeaks and other sounds made by bats but these are their social vocalizations. Like a dog whistle, their echolocation are too high for people to hear. If they were in the human hearing range they would be as loud as a jackhammer, a 747 taking off or a Heavy Metal band playing with the volume on their amplifiers turned up to 11. Echolocation of 145 decibels have been recorded. The sounds are so loud in fact that bat ears have a muscle that temporarily disconnects their ear drum when the clicks are too loud.
“The intensity and frequency of these sonar probes varies according to the bat’s needs,” Attenborough wrote. “Those for general navigation are not as intense as those which the bat makes when homing in on a particular target. All such sounds are reflected back from surrounding objects and received by the bats’s large ears which also vary in shape from species to species. These echoes, are, of course, very faint, as a bat’s sense of hearing has to be extremely sensitive. If the bat hears it shrieks with its own hyper-sensitive ears, it would deafen itself, but it is able to switch off its sense of hearing every time it emits a stab of sound. And it has to do that as frequently as two hundred times a second.”
Sometimes people can feel echolocation from bats if they get close enough. The range of detection for bats is generally a few feet to several yards. The higher the pitch the smaller the surface of the echo. The louder the clicks the more distant an object is. The more frequent the clicks the more up to date the information the bat receives,. Some bats can emit clicks at a rate of two hundred a second and decipher each click.
Feeding Bats
Bats feed on insects, fruits, small animals, and nectar. Some species eat two and half times their body-weight every night and digest their meals in as little as 15 minutes. Most either eat insects or fruit and nectar. A few feed on fish, frogs, birds and rodents. Some bats have even been observed eating other species of bat.
Insect-eating bats often hunt most aggressively around dusk and before dawn. When the weather is warm they hunt all night. It often seems like they fly around erratically. But that is not the case. Most catch insects in mid air and dart around, this way and that way, as they pursue insects, sometimes at a rate of 1000 an hour. Most insect-eating bats catch their prey in their mouth or by deflecting it into their mouths with their wings. Some snatch beetles and roach on the ground.
Insect-eating bats eats huge amounts of insects, including many mosquitos and other pests. It estimated that in area the size of Texas they consume 200,000 tons of insects a year. A single brown sky bat can down up to 600 insects an hour. A 20-million-member colony can consume 250 tons of insects every night.
Some bats have sharp teeth from ripping into animals or fruit. Some species can swallow pieces as large as their head whole, licking their chops when they are done. Species that feed on nectar have long tongues to slurp up nectar. Sometimes their tongues are as long as their bodies. To attract them flowers bloom at night and produce a musky scent that attract bats and other mammals. Some bats in the Philippines drink fermenting palm sap, the alcoholic constituent of hot toddies, and can usually be identified by their "staggering flight."
Bats, Seed Dispersal and Pollination
Bats that eat fruit or feed on nectar or pollen play a major role in dispersing seeds and pollinating plants. Some species spread pollen from flowers to flower and dispense seeds over a large area and are just important to plant reproduction as birds and bees.
Bats defecate in mid air and account for up to 95 percent of aerial seed dispersal. Birds in contrast usually defecate when they are perched and as a result do not scatter seeds as widely as bats do. It is a good idea not to be in a cave near dusk. Bats usually urinate and defecate on waking up "so they will not have to take flight with a useless load." By flexing their knees they "avoid soiling themselves or their neighbors."
Studies have show that in other places where populations of bats have been reduced plants flower less and produces less fruit, which birds and mammals count on for their survival. In deforested reduced bat populations sometimes means that some species of hardwoods and fruit trees have a harder time re-establishing themselves without bats to help spread their seeds.
Bat Caves
Most bats live in colonies in trees and caves but can also be found sleeping in buildings, tree hollows, boulder heaps, culverts, attics, belfries, abandoned animal burrows, thatch, bird's nest, under bridges, in the open. Some species cut leave and produced sophisticated "tents" or nest in spider webs.
Bats are most numerous in the tropics, where there are caves with literally millions of bats. They play a very important role in the rain forest where many species of plant rely on specific species of bat for pollination. Many bats in temperate latitudes hibernate in caves in the winter. However sometimes when the weather is mild they emerge for a quick feed and go back to sleep.
Bats that live in caves are often very particular about the conditions of the caves they occupy. They have to be dry, not too cold and have a steady temperature. Generally these caves are not very welcoming to humans. The strong stench of ammonia from the droppings on the floor can be overwhelming. The droppings themselves and sticky muck on the floor can be disgusting to walk through. Bring rubber boots if you ever venture into such a place. Rain gear is advised for the stream of urine and feces that drop from the roof.
See Malaysia, Places.
Bat Mating and Child-Rearing
Male bats honk and make chirping noise to lure females. The males of some species have harems of eight or nine females which they change every day. After ejaculating sperm the male bat produces a kind of wax which seals the female's orifice and prevents competitors from impregnating the female.
Unlike birds which lay eggs and thus are relived of the burden of carrying the load of a baby, bats like all mammals carry a developing fetus within them. As a consequence twins are a rarity and females generally give birth to one young a season. To compensate for this bats must breed and live a relatively long time — up to 20 years, which is long for such a small animal — to keep their population numbers up.
Sometimes millions of only female bats gather in caves to raise their young. Some 20 million female freetailed bats move into Bracken Cave in Texas in the summer leaving their mates 1000 miles behind in Mexico. It is not known exactly why the female bats congregate like this.
Some bat species that have difficulty giving birth are assisted by female bat “midwives.” The midwives help the laboring mother by demonstrating the correct position for her to be in and imitating the strains new mother will have to endure.
Female bats have their nipples in their armpits. Bats continue nursing their offspring until they are almost fully grown because young bats need a lot of time to develop their wings to fly. Bat pups can weigh up to too a quarter of the weight of their mothers, who often fly through the air with their young clinging to their bodies.
Mother Bats Locating Their Young
Mother bats often leave their young with several thousand other young bats and then pick them out in the evening when they return. There is a lot of jostling among the young and individual bats rarely remain the same place for long. It was though for a long time that the mothers could not pick out their offspring from the others and simply suckled the first young bat they came to. Genetic studies have shown this is not the case.
After hunting for hours a mother returns to the approximate place she earlier left her young. She can tell here young from the hundreds or thousands of others by her’s young call. To locate her offspring the mothers calls her young and identifies them by their unique response. The young squeal, yelp, grunt and trill and produce a wide range of sounds at a variety of pitches, volumes, frequencies and lengths.
There is a great deal of commotion as the mother locates her young. Other young bat try to suck from breasts as she searches. Finally when she locate her offspring she opens her wings and lets it suckle in her armpit.
Bats and Humans
Bats help humans by eating mosquitos and other pests. They are especially useful to farmers eating insects that damage crops. Bats are also eaten in a number of places. It has been said that they taste like partridge. In Ivory Coast there is large market for selling hunted bats. People also eat them in the Philippines and Indonesia. In Guam people pay as much as $25 for a single bat.
Bats are often blamed for eating fruit trees in orchards but studies have shown that monkeys are often the culprits not bats. Fruit-eating bats only eaten ripened fruit, which is no skin off a framers back because he usually ships off his produce weeks before it is ripe so it will be ripe when it is in the store. Bat apparently don't like unripened fruit any more than humans do.
Bats can be easily killed in places where they roost. A single shotgun blast can kill 20 to 60 roosting bats. Sometimes they are killed by the thousands by covering up their caves so they can’t feed. Because females only have one or two offspring a year it takes a while for a population of bats to recover once members are killed or their cave has been disturbed. Bat deaths can also have a serious on the ecosystem they are part of.
The only other predators that bats have to worry about other than man are snakes and predatory birds like eagles and hawks that sometimes snatch the tree-roosting bats while they are sleeping during the day.
Bats and Disease
Bats are blamed for spreading a number of rare, serious diseases to humans such the Lyssa virus which has killed people in the Ukraine and Britain; the Nipah virus in Malaysia See Malaysia); and the Hendra virus in Australia (See Australia); and the ALS-Parkinson dementia complex in Guam. In the later case, the Chamorro on Guam were more 100 times likely to develop ALS-Parkinson dementia complex than other people. It was found that those affected had eaten fruit bats that were full of neurotoxins picked up from feeding on seeds of cyad plants. People also get rabies from bats. Vampire bats are notorious for that.
In the mid 2000s, bats in some part of the United States began dying of a strange unknown disease. Many of the victims flew around in winter in the day (in temperate climates bats hibernate in winter and normally bats only fly around at dusk and night) and were found with white fungus on their bodies. In some caves in New York 90 percent of the bats that hibernated there died. No one knew whether the disease was caused by a virus, bacteria, toxin, environmental agent or metabolic disorder produced by fungus. The fungus is believed to have been a secondary symptom.
Studying Bats
Yale University's Alvin Novick has spent the better part of his life studying bats in locations around the globe: tall trees in the Philippines, rain forests in Africa and caves in Jamaica. He has studied vampires bats, flying foxes, and moustache bats. His favorite places to find bats are attics, which unfortunately become very flimsy after termites or dry rot sets in: "I've fallen through ceilings around the world," he boasts.
Novick catches bats in caves with fishing net; in the rain forest with a net draped in between trees. Captured bats are studied in echo-absorbing chambers were scientists sometimes hook up electrodes to bat brains to listen in. During the 1970s Novick was working on "bat dictionary" that classified bat species by the sounds they admitted.
Catching bats can be dirty, nasty work. Describing an effort to snag some spear-nosed bats in an abandoned gold mine Panama, Novick wrote in National Geographic: "I was standing there naked. I wanted to capture several bats...Every morning for half a century hundred of bats have flown back to this roost bearing morsels of fruit, which they often dropped into the water along with their guano. All this brewed into a pungent mix the color and consistency of thin chocolate pudding...Stripped except of my flashlight I wadded in...My light shone on the hanging bats...they became disoriented and crashed into the walls, the pudding and me...a rain of dozens of bats smashing wild into my face...I ducked. I found myself chin deep in the soup and verging on nausea...I downed by emotions, rose dripping from the gumbo, capturing my quarry, and moving out swiftly.”
Flying foxes that are studied by scientists are caught with nets and outfit with radio collars.
Image Sources:
Text Sources: Mostly National Geographic articles. Also “Life on Earth” by David Attenborough (Princeton University Press), New York Times, Washington Post, Los Angeles Times, Smithsonian magazine, Natural History magazine, Discover magazine, Times of London, The New Yorker, Time, Newsweek, Reuters, AP, AFP, Lonely Planet Guides, Compton’s Encyclopedia and various books and other publications.
Last updated March 2011