Essay, Research Paper: Bats

By Nick Carroll (I do not wish to remain anonymous; let my work benefit everyone!!)
Note: I wrote this as a freshman. I do not know if it is any good. The information is accurate, though. Have Fun!


Bats: Their Life and Special Senses

Bats are the only mammals capable of long periods of flight. Bats are classified into two distinct groups, larger bats, or megabats and smaller bats, called microbats, in 17 families. One of these families contain all megabats (more than 150 species); the other 16 families are microbats. Roughly 900 species of bats exist, far more than in any other order of mammals with the possible exception rodents, which bats probably exceed in sheer numbers.
Distribution

Bats inhabit areas worldwide except in extreme cold conditions such as Arctic regions. All megabats in addition to some microbats are live only in the eastern hemisphere, while other microbats live only in the western hemisphere. Some families of microbats exist globally. Four families of microbats live in temperate regions, while the number of resident species diminishes poleward. Members of only two families reach subarctic regions, and then only in the summer.

Flight

The ability of true flight in vertebrates is completely indigenous to most birds and all bats. The flight ability of the bat, however, is much more maneuverable and able to fly at lower altitudes. A thin membrane makes up the wing, supported near its leading edge by the extended bones of the forelimb and second finger, and toward the ends of the third, fourth, and fifth fingers. It is attached along the midline of the trunk and outward-directed legs, and in various species it extends between legs and tail. Only the first finger, or thumb, is free, and in most bats it alone is clawed, together with the toes. This structure enables bats to vary the convexity of the wings dramatically and thus vary their aerodynamic lift.

Echolocation in Bats

All microbats navigate, and most species that feed primarily on insects also target their prey through the process of echolocation. This is the emission of pulses of high-frequency sounds that are reflected back as echoes to a bat's ears from surrounding surfaces, indicating the position, relative distance, and even the character of objects in its environment. In this sense microbats "see" with the use sound. This is the reason that bats have the ability to navigate in pure darkness. Physical properties of the sounds emitted vary in characteristic ways among the different species. The sound pulses are generated in the larynx, and are emitted via the mouth or the nose depending on the species of bat itself.
In contrast to microbats, most megabats use vision rather than acoustics for orientation. There is only one genus of megabat that has evolved an echolocation mechanism, involving the emission of audible clicking noises, and it is used only when the bats fly in darkness , as even they operate primarily with optics. The eyes of megabats are also relatively larger than those of microbats, helping them to see better. No bat is blind, however, and even echolocating microbats may use gross visual landmarks for homing during flight. Many bats are color blind however.

Behavior

Microbats are nocturnal, with the exception of a small few. During the day they may rest in a variety of roosting places, such as caves, crevices, hollow trees, foliage, hiding places beneath rocks or bark, and in buildings. They may even roost in exposed situations; certain larger megabats hang upside down in enormous aggregations from tree branches. Nocturnality gives bats many advantages, such as greatly reduced competition for insects and other food items, substantial freedom from attack, and protection from overheating and dehydration, to which bats are especially liable because of their enormous skin area relative to their size.
A few species of bats live solitarily, but most are gregarious. Aggregation during the day may vary from small groups consisting of a single male and a dozen or more females to enormous assemblages numbering many thousands or even millions of individuals. Aggregations of members of specific species may show seasonal variation and sexual segregation in varying combinations. Mixed-species associations of a casual sort are common among bats using protected shelters such as caves.
Certain species of Temperate Zone bats are migratory to some degree, and movements of nearly 1600 km between summer and winter quarters have been recorded. Others may fly only a few or up to 40 km or more daily between roosting and feeding sites, but the majority forage within more restricted home ranges.
Most bats are insectivorous and are able to catch their prey in flight or to seek out stationary insects on foliage or other surfaces. Most megabats, and many species of leaf-nosed bats of tropical America (so named for the remarkable folds of skin projecting upward from the nose), are fruit eaters. Still others in both groups consume flower parts or extract the nectar from flowering plants by means of greatly elongated tongues, aiding cross-pollination of the plants in the process. Some of the larger leaf-nosed bats as well as members of one Eurasian family are carnivorous or omnivorous; they attack small amphibians, lizards, birds, mice, and even other bats, in addition to consuming insects and fruit. Closely related to the leaf-nosed bats are the true vampires of the American Tropics, which subsist entirely on blood freshly drawn from small wounds inflicted on mostly warm-blooded prey such as fowl, cattle, horses, swine, and occasionally human beings. At least three species of bats supplement their diets with small fish, which are caught as the flying bats drag their enlarged feet and claws just beneath the water surface.