The Bat

Dec 06, 2009 Features / Columnists, Interesting Creatures in Guyana

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Bats are flying mammals in the order Chiroptera. The forelimbs of bats are webbed and developed as wings, making them the only mammals naturally capable of true and sustained flight. By contrast, other mammals said to fly, such as flying squirrels, gliding possums and colugos, glide rather than fly, and only 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.
There are about 1,100 bat species worldwide, which represent about 20 percent of all classified mammal species. About 70 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.
The appearance and flight movement of bats 52.5 million years ago were different from those of bats today. Some had claws on all five 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. The 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, some alternated between flaps and glides while in the air. Such physical characteristics suggest that some 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. Bats are mammals. Sometimes they are mistakenly called “flying rodents” or “flying rats,” and they can also be mistaken for insects and birds.
There are two suborders of bats: Megachiroptera (megabats) and Microchiroptera (microbats/echolocating bats). Megabats eat fruit, nectar or pollen while most microbats eat insects; others may feed on the blood of animals, small mammals, fish, fruit, pollen or nectar. Megabats have a well-developed visual cortex and show good visual acuity, while microbats rely on echolocation for navigation and finding prey.
The phylogenetic relationships of the different groups of bats have been the subject of much debate. The traditional subdivision between Megachiroptera and Microchiroptera reflects the view that these groups of bats have evolved independently of each other for a long time, from a common ancestor that was already capable of flight. This hypothesis recognized differences between microbats and megabats and acknowledged that flight has just evolved only in one order of mammals.
Most molecular biological evidence supports the view that bats form a single or monophyletic group. Researchers have proposed alternate views of chiropteran phylogeny and classification, but more research is needed.
Most bats have a breeding season, which is in the spring for species living in a temperate climate. Bats may have one to three litters in a season, depending on the species and on environmental conditions such as the availability of food and roost sites. Females generally have one offspring at a time, this is maybe a result of the mother’s need to fly to feed while pregnant. Female bats nurse their youngster until it has grown nearly to adult size, this is because a young bat cannot forage on its own until its wings are fully developed.
Female bats use a variety of strategies to control the timing of pregnancy and the birth of young, to make delivery coincide with maximum food ability and other ecological factors. Females of some species have delayed fertilisation, in which sperms are stored in the reproductive tract for several months after mating. In many such cases, mating occurs in the fall, and fertilisation does not occur until the following spring.
Other species exhibit delayed implantation, in which the egg is fertilised after mating, but remains free in the reproductive tract until external conditions become favourable for giving birth and caring for the offspring.
In yet another strategy, fertilisation and implantation both occur but development of the foetus is delayed until favourable conditions prevail. All of these adaptations result in the pup being born during a time of high local production of fruit or insects. At birth wings are too small to be used for flight. Young microbats become independent at the age of six to eight weeks, megabats do not until they are four months old. A single bat can live over 20 years, but the bat population growth is limited by the slow birth rate.
(Source: Wikipedia – The Free Online Encyclopedia)

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