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10 November 2007

Taman Negara's rich cave ecosystem | The Brunei Times
Tropical cave fauna in Malaysian caves

Taman Negara's rich cave ecosystem

Getting bats: Animals found in Malaysian caves range from tiny microscopic organisms invisible to the naked eye right through to elephants, but the cave racer snake is at the top of the food chain, feeding exclusively on bats and swiftlets. Picture: Liz Price
Sunday, November 4, 2007
MY MOST terrifying night was the one I spent alone in a cave in Taman Negara. I was kept awake by fears of wild animals, my imagination running riot. Several times during that long night, I saw porcupines walking past, but to my surprise they took no notice and carried on their nocturnal wanderings as if I wasn't there. Fireflies occasionally flew past, their eerie green glow startling me at first.

My main fear, however, was of tigers and elephants. Would I provide a handy meal for a tiger? Or would I be trampled underfoot by an elephant? Elephants at Taman Negara regularly visit caves, although it is not really known why. Maybe they visit to lick salts, like their relatives in the Kitum Caves, Kenya. Although I saw neither tiger nor elephant, I was greeted by a steaming pile of elephant dung only a few metres away when I left the cave in the morning.

Animals found in Malaysian caves range from tiny microscopic organisms invisible to the naked eye right through to elephants. However not all these creatures are troglobites or cave dwellers. Some are troglophiles (animals found in caves but which can also live outside); others are trogloxenes (cave dwellers which go outside to feed). Cave visitors include man and elephants.

Studies on the cave fauna in Malaysia began in 1898 when Ridley examined the Batu Caves in West Malaysia. Various other scientists followed his footsteps, sending their collections worldwide for identification. In Batu Caves alone, more than 144 species of invertebrates were found. Over in Borneo, Lord Medway has done most of the work on cave fauna, mainly in Sarawak, specialising on the bats and swiftlets.

The cave food chain is quite complex, but everything ultimately depends on the bat for survival. This is because the bats are the only creatures that leave the cave to go out and feed. There are two types of bat, the insect eaters and the fruit bats. Each night they would go out to feed on insects, fruits or pollen, and it is their guano or excreta deposited in the cave that supports the whole food chain, from the smallest bug through to the cave-dwelling snake.

The guano of the fruit bats is very nutritious compared to that of the insect bats. This can easily be seen just by looking at the life contained in the guano: the rich fruit bat's guano found near the cave entrance is absolutely heaving with life, much more so than the guano from the insect-eating bats. So the fruit bats in particular support the invertebrates.

Many people have a fear of bats, probably because of legends and Hollywood vampire films. But bats are very useful to man, especially for fruit lovers, as they help to pollinate durian and petai, which flower at night. Without the bats there would be less durians.

They also help to control the insect population. An estimated 1-2 million (maybe more) bats live in Deer Cave in Mulu. Every night they fly out to feed, each one eating at least 10g of insects during a night of hunting, so this is at least 10 tonnes of insects consumed in a single night. Can you imagine 10 tonnes of mosquitoes? This results in a few of tonnes of guano falling onto the floor each day.

Deer Cave is particularly rich in invertebrate life. Bats can be very fussy about which cave to roost in, and if conditions are not quite right they won't stay. A cave without bats means no other animals will be found. The guano is home and food to countless creatures: flies, maggots, beetles, bugs, millipedes, springtails, cockroaches, worms, mites, moths. They make the guano look as if it has a life of its own as it heaves and flows like thick liquid and, if disturbed, the creatures frantically try to bury themselves.

These animals are in turn fed upon by the cave crickets, centipedes, whip scorpions, true scorpions and spiders. And in their turn, all these provide food for small mammals, frogs and toads.

Animal carcasses, especially those of bats, are scavenged almost immediately, and soon nothing remains except the bare skeleton.

The water dwellers such as the debris feeders, larvae and flat worms are eaten by snails, fish, and crabs. Catfish can be seen in some cave rivers and there are various species of white crab, especially in Mulu and Bidi. The bats and the cave swiftlets have parasites such as mite, chiggers, ticks, fleas and flies. Particularly noticeable in Deer Cave are the Hairy Earwigs, which live on the Naked Bats, feeding on oils produced by the bats to protect their skin.

At the top of this whole food chain is the cave racer. The cave racer is the only snake that is adapted to spend its whole life in a cave, feeding exclusively on bats and swiftlets. The racer can climb walls to reach its prey, where it will rest with its head hanging out waiting for its dinner to fly past. It then constricts its prey before swallowing it. Another expert climber is the egg-eating cricket, which will climb to reach swiftlet eggs and chicks left unguarded in nests.

Other types of snakes are occasionally found in caves, especially pythons, but these have come in by accident, and cannot survive there, so we usually try to take them out. Animals using caves as a shelter include moths, fireflies and sandflies. Potter wasps and hornets built nests at cave entrances. Larger animals include rodents, porcupine, pigs, deer, leopard, serow and elephants. Sometimes domestic house cats turn feral and move into a cave.

Many people think of cave fauna as being blind and white in colour, like the Proteus salamander in Slovenia, but this is not the case. The only white troglobite is the cave crab, which is eyeless, and found in Mulu. But the Bidi cave crabs still have eyes and pigments. The blind crabs along with the millipedes and whip scorpions are apparently the only troglobites without eyes. All the others have reduced eyes and pigments.

People have mistaken the white cockroach to be a new species, whereas in fact it is only the normal cockroach which is moulting and has shed its skin. After a short while the white colour will darken to the normal brown. Near urban areas, the house cockroach is making its home in caves and seems to be taking over from the smaller, indigenous cave roach, possibly upsetting the natural balance.

Insect troglobites often have very long feelers to navigate and hunt their prey, and also elongated legs. The feelers and legs can be several times longer than the body, especially the long legged centipedes, the cricket and the whip scorpion. The only two poisonous invertebrates are the centipedes and the scorpion, both of which can also be found in the forest.

Unfortunately, man is also upsetting the balance of the cave ecosystem. Bat guano is collected from many caves for use as fertiliser. This practice has been going on for well over 100 years, and many archaeological remains have been lost through indiscriminate collection. Cockroaches are also taken from caves for bait by fishermen.

The nests of the cave swiftlets have been harvested by man for centuries to make bird's nest soup. The edible nests fetch a high price on the market: one kg of white nest costs more than US$1,700 ($2,500). In the past, the nests were collected all year round, resulting in a depletion of swiftlet numbers. Now, in many caves in Borneo, the harvest is restricted to two or three times a year to give the bird population a chance to recover. During the removal of the nests, baby birds sometimes fall to the floor and they die.

Luckily, many humans are squeamish and repelled by the sight and smell of guano, the bats and cockroaches, and therefore the casual visitor tends to avoid these caves, thereby leaving the fauna undisturbed.

But for people with a genuine interest, caves provide a fascinating place to see a whole range of fauna going about their everyday life.The Brunei Times

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