In a contest to find the animal which makes people cringe most, the bat must surely rate very high. Certainly among the first three alongside snakes and spiders.
Although the vast majority of people have never seen a bat close up - the usual view is of shadowy forms flitting about in the twilight as they catch their evening meal, most people can identify one, although they would probably have no idea which of the native species it might be.
Bats (Chiroptera) are unique in being the only group of mammals that, like birds, have sustained flight. There are about 1,117 species of bats the world over in two unequal suborders -the Megachiroptera (Mega bats or fruit bats), which consist of 186 species of old world fruit bats and the Microchiroptera (Micro bats or Insectivorous bats) which consist of 931 species in 17 families.
Bats are widely distributed, inhabiting various habitats ranging from the seaside, mountains, rainforest to deserts. And they have been recorded throughout the world excepting the Antarctic and a few Oceanic islands.
Some of the bat families are widespread and are recorded from both the old world and the new world. Others are restricted in their range and are recorded either only from the old world or new world. Of the 18 families of bats, eight families (Pteropodidae, Rhinolophidae, Hipposideridae, Myzopodidae and Mystacinidae) are restricted to the old world; six families (Noctilionidae, Phyllostomidae, Desmodontidae, Natalidae, Furipteridae and Thyropteridae) are restricted to the new world; and the remaining three families (Emballonuridae, Molossidae and Vespertilionidae) are found in both the old and new worlds.
|Black-bearded sheath tailed bat
These unique mammals have undergone extensive adaptations to different diets including fruits, nectar, blood, insects, fish, frogs, small birds and mammals.
Although little is known about the early history of bats, it is assumed that they evolved from an animal like a shrew. The oldest fossil bat is about 50 million years old and is strikingly similar in external appearance to its modern descendents. For comparison, the oldest fossils of man are only half a million years old.
Of the 1,117 species of bats found in the world, 30 species are deemed to exist in Sri Lanka, of which four belong to the suborder Megachiroptera and the remaining 26 to the suborder Microchiroptera. These bats day roost in caves, old plumbago mines, derelict buildings, roofs, trees, tree holes and amongst dead branches and leaves.
The species of mega bats that are found on the island belong to the three genera, namely Pteropus (Flying fox), Cynopterus (two species of short-nosed fruit bats) and Rousettus (dog faced fruit bat). These bats do not use echolocation apart from the genus Rousettus.
The genus Pteropus consist of the largest bats to be found in the world. The largest bat found on the island is the flying fox Pteropus giganteus, which has an average wingspan of about one metre.. These bats are frugivorous (fruit eaters). Research has shown that some flying foxes have been known to travel 70 km in search of food. They play a vital ecological role in pollinating flowers and dispersing seeds of various types of trees. Some plants solely depend on these bats to disperse their seeds.
The genus Cynopterus has an interesting little bat (Cynopter sphinx), which constructs a tent; by chewing the middle part of the leaves of Palm tree, so that they dangle giving a tent-like appearance.
This suborder Microchiroptera include the smallest bat of the subcontinent- the pigmy bat Pipistrellus tenuis which has an average body weight about 2 grams and the most striking bat of the country the painted bat Kerivoula picta locally known as Kesel Voula.
The suborder is represented by six families of bats, namely Emballonuridae (Sheath-tailed bats), Hipposideridae (Leaf-nosed bats), Megadermatidae (False vampire bats), Molossidae (wrinkled-lipped bats), Rhinolophidae (Horse-shoe bats) and Vespertillionidae (Evening bats).
In flight, these bats make the average bird look a rank amateur with their incomparable skill and manoeuvrability. They stop, turn at right angles in mid-air, change direction in seemingly impossible ways, and of course they have the added refinement of built-in echo location systems which virtually eliminate the danger of collision with any obstacles.
Bat hunt at night; they do not listen for the sounds made by the prey; rather, they produce their own, very high frequency sounds and listen for the echoes that bounce back, so the face of many bats is dominated by sonar equipment, elaborate translucent ears, ribbed with cartilage and laced with an internal tracery of scarlet blood vessels; the noses of some species are so complex, species of horse-shoe bats, false vampire bats and leaf-nosed bats have complex nose leaves in all sorts of shape and sizes (leaves, spikes and spears) to direct the sound.
The nostrils from which, the ultra sound are emitted in a narrow beam, are situated in the middle of this nose leaf. Some emit ultrasound through their mouths. Each species has its own pattern, so that each can produce a unique call.
Receptors matched to it alone filter out signals from other species. When a micro bat forages at night and locates an insect by means of echo location it hones in on it, increasing the rate with which sounds are emitted up to 200 times a second.
A victim such as a beetle is then seized and eaten, or, if too large for immediate consumption, flicked by the wing into the interfemoral membrane which is brought up underneath the abdomen to form a pouch.
A highly effective brown bat (Myotis hasseltii) can capture and eat about 3000 insects in a single night.
Decline of bats
Declining numbers of bats have been recorded in surveys from all over the island. The decline is sufficiently serious for the relevant authorities to pass legislation to protect them. In some areas certain species have been extinguished and in others the population is much reduced.
The causes for their decline are manifold. They include the use of pesticides to which Microchiroptera bats are especially susceptible as the pesticides accumulate inside their prey and are transferred to the bats, which eventually die, do to poisoning.
Bats are also eaten in certain parts of the island, people even eating the Microchiroptera bats of which some only weigh between 10-20 grams.
Another serious threat is habitat destruction, the felling of trees, disturbance to the roosting caves and demolition of old houses etc.
People should be made aware to the crucial role bats play in insect control and pollination. They help control pests as some bats eat half their weight in insects in one night.
In some countries, even disturbing a bat or its roost can be a punishable offence with a heavy fine. Bats can be a tourist attraction like in other countries. In Texas for example, the Congress Avenue bridge in Austin is home to North America’s largest urban bat colony, an estimated 1,500,000 Mexican free-tailed bats, which eat an estimated 10,000 to 30,000 pounds of insects each night. An estimated 100,000 tourists visit the bridge to watch the bats leave the roost each year.
Sri Lanka is home to a much wider variety of bats and we also have cave complexes such as Vaulpane, Vaulgalge of Koslanda etc. that are home to cave dwelling bats where some species are found in their thousands. It is upto us then to protect these flittering mammals.
(The writers are members of the Bio-Diversity Education and Research unit of the Young
Biologists' Association )