|
Chiroptera:
Bats are mammals in the order Chiroptera. Their most distinguishing feature is that their forelimbs are developed as wings, making them the only mammal in the world naturally capable of flight; other mammals, such as flying squirrels and gliding phalangers, can glide for limited distances but are not capable of true sustainable flight. The word Chiroptera can be translated from the Greek words for "hand wing," as the structure of the open wing is very similar to an outspread human hand, with a membrane (patagium) between the fingers that also stretches between hand and body. There are estimated to be about 1,100 species of bats worldwide, accounting for about 20% of all mammal species. About 70% of bats are insectivores. Of the remainder, most feed on fruits and their juices; three species sustain themselves with blood and some prey on vertebrates. These bats include the leaf-nosed bats (Phyllostomidae) of central America and South America, and the related bulldog bats (Noctilionidae) that feed on fish. At least two known species of bat feed on other bats: the Spectral Bat or American False Vampire bat and the Ghost Bat of Australia. Despite the cold weather, there are 5 species of bats in Alaska. Some of the smaller bat species are important pollinators of some tropical flowers. Indeed, many tropical plants are now found to be totally dependent on them, not just for pollination, but for spreading their seeds by eating the resulting fruits. This role explains environmental concerns when a bat is introduced in a new setting. Classification and Evolution:
Bats are mammals. Though sometimes called "flying rodents", "flying mice," or even mistaken for bugs and birds, bats are neither mice nor rodents, and certainly not arthropods. There are two suborders of bats: 1.Megachiroptera (megabats)
2.Microchiroptera (microbats/echolocating bats)
Despite the name, not all megabats are larger than microbats. The major distinction between the two suborders is based on other factors.
1.Microbats use echolocation, whereas megabats do not (except for Rousettus and relatives, which do). 2.Microbats lack the claw at the second toe of the forelimb. 3.The ears of microbats do not form a closed ring, but the edges are separated from each other at the base of the ear.
4.Microbats lack underfur; they have only guard hairs or are naked. 5.Megabats eat fruit, nectar or pollen while microbats eat insects, blood (small quantities of blood of animals), small mammals, and fish, relying on echolocation for navigation and finding prey. Genetic evidence indicates that some microbats ("Yinochiroptera") are more closely related to megabats than to the other microbats ("Yangochiroptera"). There is some morphological evidence that Megachiroptera evolved flight separately from Microchiroptera; if so, the Microchiroptera would have uncertain affinities. When adaptations to flight are discounted in a cladistic analysis, the Megachiroptera are allied to primates by anatomical features that are not shared with Microchiroptera. Little is known about the evolution of bats, since their small, delicate skeletons do not fossilize well. However a late Cretaceous tooth from South America resembles that of an early Microchiropteran bat. The oldest known definite bat fossils, such as Icaronycteris, Archaeonycteris, Palaeochiropteryx and Hassianycteris, are from the early Eocene (about 50 million years ago), but they were already very similar to modern microbats. Archaeopteropus, formerly classified as the earliest known megachiropteran, is now classified as a microchiropteran.
Bats are traditionally grouped with the tree shrews (Scandentia), colugos (Dermoptera), and the primates in superorder Archonta because of the similarities between Megachiroptera and these mammals. However, molecular studies have placed them as sister group to Ferungulata -- a large grouping including carnivorans, pangolins, odd-toed ungulates, even-toed ungulates, and whales. Anatomy:
By emitting high-pitched sounds and listening to the echoes, microbats locate prey and other nearby objects. This is the process of echolocation, an ability they share with dolphins and whales. Two groups of moth exploit the bats' senses: tiger moths produce ultrasonic signals to warn the bats that the moths are chemically-protected (aposematism) (this was once thought to be a form of "radar jamming", but this theory has been disproved); 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 maneuvers. Although the eyes of most microbat species are small and poorly developed, their sense of vision is typically very good, especially at long distances, beyond the range of echolocation. Their senses of smell and hearing are excellent. The teeth of microbats resemble those of the insectivorans. They are very sharp in order to bite through the hardened armour of insects or the skin of fruits. While other mammals have one-way valves only in their veins to prevent the blood from flowing backwards, bats also have the same mechanism in their arteries. 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 instead of circular as is the bone in a human finger, making it even more flexible. The skin on their wing membranes is a lot more elastic and can stretch much more than what is usually seen among mammals.
Because their wings are much thinner than those of birds, bats can maneuver more quickly and more precisely than birds. The surface of their wings are also equipped with touch-sensitive receptors on small bumps called Merkel cells, found in most mammals, including humans. But 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. 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.
Reproduction:
Mother bats usually have only one offspring per year. A baby bat is referred to as a pup. Pups are usually left in the roost when they are not nursing. However, a newborn bat can cling to the fur of the mother and be transported, although they soon grow too large for this. It would be difficult for an adult bat to carry more than one young, but normally only one young is born. Bats often form nursery roosts, with many females giving birth in the same area, be it a cave, a tree hole, or a cavity in a building. Mother bats are able to find their young in huge colonies of millions of other pups. Pups have even been seen to feed on other mothers' milk if their mother is dry. Only the mother cares for the young, and there is no continuous partnership with male bats.
The ability to fly is congenital, but after birth the wings are too small to fly. Young microbats become independent at the age of 6 to 8 weeks, megabats not until they are four months old. At the age of two years bats are sexually mature. A single bat can live over 20 years, but the bat population growth is limited by the slow birth rate.
Habits and Behaviour:
Most microbats are active at night or at twilight.
The social structure of bats varies, with some bats leading a solitary life and others living in caves colonized by more than a million bats. The fission-fusion social structure is seen among several species of bats. The fusion part is all the individuals in a roosting area. The fission part is the breaking apart and mixing of subgroups by switching roosts with bats, ending up with bats in different trees and often with different roostmates.
Studies also show that bats make all kinds of sounds to communicate with others. Scientists in the field have listened to bats and have been able to identify some sounds with some behavior bats will make right after the sounds are made.
|
