BATS, CHARACTERISTICS, FLIGHT, REPRODUCTION

BATS

"Chiroptera" from Ernst Haeckel's Kunstformen der Natur, 1904

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 are not blind. They are not rodents. They will not suck your blood — and most do not have rabies. Bats play key roles in ecosystems around the globe, from rain forests to deserts, especially by eating insects, including agricultural pests.

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: Animal Diversity Web animaldiversity.org ; BBC Earth bbcearth.com; A-Z-Animals.com a-z-animals.com; Live Science Animals livescience.com; Animal Info animalinfo.org ; Encyclopedia of Life eol.org , a project to create an online reference source for every species; World Wildlife Fund (WWF) worldwildlife.org the world’s largest independent conservation body; National Geographic National Geographic ; Endangered Animals (IUCN Red List of Threatened Species) iucnredlist.org ; 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

homologous skeletal structures of bat and mouse

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).

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.

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.

According to CNN: Bats have “incredible” reproductive biology that has been difficult to study given the nocturnal and secretive nature of many bat species, said study coauthor Nicolas Fasel, a bat specialist at the University of Lausanne in Switzerland. “Most of the time you’ll see their backs on the wall, and you don’t see what’s really happening in front,” he said. Teri Orr, an assistant professor and specialist in bat reproductive systems at New Mexico State University, said: “Bats do a lot of extreme things during reproduction from storing sperm to extending the duration of a pregnancy.” [Source: Katie Hunt, CNN, November 22, 2023]

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.

Image Sources: Wikimedia Commons

Text Sources: Mostly National Geographic articles. Also David Attenborough books, Live Science, 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 November 2024