Bats are flying mammals in the order Chiroptera (pronounced ). The arms of bats are webbed and developed as wings, making them the only mammals naturally capable of true and sustained flight. By contrast, other mammals can glide such as flying squirrels, gliding possums and colugos for short distances. Bats do not flap their entire forelimbs, like birds, but instead flap their spread out digits, which are very long and covered with a thin membrane or patagium. Chiroptera comes from two Greek words, cheir (χειρ) "hand" and pteron (πτερον) "wing."
There are about 1,100 bat species worldwide, which represent about twenty percent of all classified mammal species. About seventy percent of bats are insectivores. Most of the rest are frugivores, or fruit eaters. A few species feed from animals other than insects. Bats are present throughout most of the world and perform vital ecological roles such as pollinating flowers and dispersing fruit seeds. Many tropical plants depend entirely on bats for the distribution of their seeds.
Bats range in size from Kitti's Hog-nosed Bat measuring 29–33 mm (1.14–1.30 in) in length and 2 g (0.07 oz) in mass, to the Giant Golden-crowned Flying-fox which has a wing span of 1.5 m (4 ft 11 in) and weighs approximately 1.2 kg (3 lb).
Fossil bats Edit
There are few fossilized remains of bats, as they are terrestrial and light-boned. An Eocene bat, Onychonycteris finneyi, was found in the fifty-two-million-year-old Green River Formation in South Dakota, United States, in 2004 and was added as a new genus and placed in a new family when published in Nature in 2008. It had characteristics indicating that it could fly, yet the well-preserved skeleton showed that the cochlea of the inner ear lacked development needed to support the greater hearing abilities of modern bats. This provided evidence that flight in bats developed well before echolocation. The team that found the remains of this species, named Onychonycteris finneyi, recognized that it lacked ear and throat features present not only in echolocating bats today, but also in other known prehistoric species.
Fossil remains of another Eocene bat, Icaronycteris, were found in 1960.
The appearance and flight movement of bats 52.5 million years ago were different from those of bats today. Onychonycteris had claws on all five of its fingers, whereas modern bats have at most two claws appearing on two digits of each hand. It also had longer hind legs and shorter forearms, similar to climbing mammals that hang under branches such as sloths and gibbons. This palm-sized bat had broad, short wings suggesting that it could not fly as fast or as far as later bat species. Instead of flapping its wings continuously while flying, Onychonycteris likely alternated between flaps and glides while in the air. Such physical characteristics suggest that this bat did not fly as much as modern bats do, rather flying from tree to tree and spending most of its waking day climbing or hanging on the branches of trees.
Bat echolocation is a perceptual system where ultrasonic sounds are emitted specifically to produce echoes. By comparing the outgoing pulse with the returning echoes the brain and auditory nervous system can produce detailed images of the bat's surroundings. This allows bats to detect, localize and even classify their prey in complete darkness. At 130 decibels in intensity, bat calls are some of the most intense airborne animal sounds.In order to clearly distinguish returning information, bats need to be able to separate their calls from the echoes they are receiving. Within the former microbats there are two distinct approaches.1.Low Duty Cycle Echolocation: Bats can separate their calls and returning echos in time. Bats that use this approach time their short calls to finish before echoes return. This is also important because these bats contract their middle ear muscles when emitting a call in order to avoid deafening themselves. The time interval between call and echo allows them to relax these muscles so they can clearly hear the returning echo.2. High Duty Cycle Echolocation: Bats emit a continuous call and separate pulse and echo in frequency. The ears of these bats are sharply tuned to a specific frequency range. They emit calls outside of this range to avoid self-deafening. They then receive echoes back at the finely tuned frequency range by taking advantage of the Doppler shift of their motion in flight. These bats must deal with changes in the Doppler shift due to changes in their flight speed. They have adapted to change their pulse emission frequency in relation to their flight speed so echoes still return in the optimal hearing range.The new Yinpterochiroptera and Yangochiroptera classification of bats that are supported by molecular evidence, suggest two possibilities for the evolution of echolocation. It may have been gained once in a common ancestor of all bats and was then subsequently lost in the Old World fruit bats, only to be regained in the Horse-Shoe bats; or echolocation was evolved independent in both the Yinpterochiroptera and Yangochirpotera lineages.Two groups of moths exploit a bat sense to echolocate: tiger moths produce ultrasonic signals to warn the bats of that moths are chemically-protective or aposematic. This was once thought to be the biological equivalent of "radar jamming", but this theory has yet to be confirmed. The moths Noctuidae have a hearing organ called a tympanum which responds to an incoming bat signal by causing the moth's flight muscles to twitch erratically, sending the moth into random evasive manoeuvres.
Although the eyes of most microbat species are small and poorly developed, leading to poor visual acuity, none of them are blind. Vision is used to navigate microbats especially for long distances when beyond the range of echolocation. It has even been discovered that some species are able to detect ultraviolet light. They also have a high quality sense of smell and hearing. Bats hunt at night to avoid competition with birds, and travel large distances at most 800 km, in their search for food.
The finger bones of bats are much more flexible than those of other mammals. One reason is that the cartilage in their fingers lacks calcium and other minerals nearer the tips, increasing their ability to bend without splintering. The cross-section of the finger bone is also flattened compared to the circular cross section that human finger bones have, and is very flexible. The skin on their wing membranes has more elasticity and so can stretch much more than other mammals.
The wings of bats are much thinner than those of birds, so bats can manoeuvre more quickly and more accurately than birds. It is also delicate, ripping easily.However the tissue of the bat's membrane is able to regrow, such that small tears can heal quickly. The surface of their wings is equipped with touch-sensitive receptors on small bumps called Merkel cells, found in most mammals including humans, similarly found on our finger tips. These sensitive areas are different in bats as each bump has a tiny hair in the center, making it even more sensitive and allowing the bat to detect and collect information about the air flowing over its wings, thereby providing feedback to the bat to change its shape of its wing to fly more efficiently. Some bats like the little brown bat can use this dexterious ability where it is able to drink in mid air. Other bats such as the flying fox or fruit bat gently skim the water's surface, then land nearby to lick water from their chest fur.An additional kind of receptor cell is found in the wing membrane of species that use their wings to catch prey. This receptor cell is sensitive to the stretching of the membrane.The cells are concentrated in areas of the membrane where insects hit the wings when the bats capture them.
The teeth of microbats resemble insectivorans. They are very sharp to bite through the hardened armor of insects or the skin of fruit.
Mammals have one-way valves in veins to prevent the blood from flowing backwards, but bats also have one-way valves in arteries.
One species of bat has the longest tongue of any mammal relative to its body size. This is beneficial to them in terms of pollination and feeding. Their long narrow tongues can reach deep into the long cup shape of some flowers. When their tongue retracts, it coils up inside their rib cage