Tom’s Note: Probably one of the most awesome spectacles of the natural world is watching the bats leave the great cave at Niah. You must plan a trip for those who have not seen the show!
300,000 Bats
There are seven species of bats in the large cave at Niah. They are the Cave Fruit bat, Bent winged bat, Mouse-eared bat, Naked bat, the Tomb bat and the lesser and greater Horseshoe bats.
The Cave Fruit bat is the only fruit-eating bat, while the rest eat insects. The predominant species is the Lesser Horseshoe bat, which has about 220-250,000 bats. The Naked Bat makes up about 18-20,000 bats, with 5,000 of the greater Horseshoe bat and perhaps 10,000 Bent winged bats. The population of the Cave Fruit bat is probably 20,000.
The Cave
The height of all primary chambers is over 100 feet tall, with light becoming dimmer as one moves away from the mouth of the cave. Only rooms deep in the cave are wholly dark.
Various rock formations are found. In most places, the walls are smooth, and their contours are broken by blunt at the line in the change of the curve. In many places, the rock face is rough and irregular. Small blind chimneys are found where the Bent Wing
bats roost in clusters. The roofs are more or less horizontal, interrupted by sudden vertical lines, deep fissures or arched in a series of domes.
Each mouth has stalactites. There are a few complete pillars which affect the flight path of the bats. Small white spikes dip down from the roof.
Several water drips from the roof, and many others appear after a rain. Few insignificant streams and occasional guano bogs form after the dripping water.
Deep in the cave, in the dark, the humidity is rarely 1 point below saturation, and the rock surface is covered with a rough grey slimy coating several mm thick and wipes of exposing the white stone underneath. This coating depends on the high humidity as the airy areas are dry, rough and uncoated.
The temperature varies very little. Temperature variation was between 76.5 and 77. 5 F. The big caverns are less well insulated and are influenced by temperature fluctuations outside the cave.
The Bats
The Bats do not roost throughout the cave. The intensity of daylight seems to be the limiting factor. All the bats are light shy and shy away from sunlight that supports green algal growth.
It is the intermediate zone where most of the bats roost. All species except the Mouse-eared bat frequent the dry uncoated rock in the big chambers. Most of the lesser Horseshoe bats are found here, scattered over a wide variety needing only surface roughness or minor irregularities to hold their tiny feet and sharp claws. The one colony of Naked bats is sited in this dimly lit zone high on the ceiling, along with the five crowded roosts of the Cave Fruit bat.
Lesser Horseshoe bats are found in the zone with high humidity and coated cave walls, but only at regular roosting sites where their claws keep the rock surface clean and rough. These spots stand out as pale patches in the general creamy grey of the coated stone. Every day, a single bat hangs near the centre; if disturbed, it flies away but returns to its particular roost.
In the intermediate zone, the Greater Horseshoe is shy as it is not seen on the open walls of the aisles of the bi chamber but only in the recesses, in the lower dome “side chapels”. The slime does not deter it. The bat has a foot twice as large as the Lesser Horseshoe. It is presumably undeterred by the slimy coating of the interior walls.
The Bent winged bats can be found at roost on the open wall of dark, secluded tunnels and grottos. It typically occurs in groups of one to five clustered at the top dead centre of the small blind chimney. It prefers the darker and totally dark regions appearing still shyer of light than the Greater Horseshoe. The five Mouse-eared bats recorded were also in the chimney sites. In this way, each species has its own roosting habits, which rarely conflict. The six kinds of bats exist quite independently without competition from the other.
The Cave Fruit Bat and the Naked Bat both form tight colonies chattering and calling continuously high in the roof of the main chamber. The Cave Fruit has five different colonies, while the Naked Bat are arranged in one dense group. The Bent wing group collect in smaller clusters with a single male servicing four females.
Allowing for the difference in behaviour between the species, there is a pattern common to bats leaving the cave. Apart from early fliers and rare late stragglers, they build up to a high rate within a few minutes and continue fairly steadily until they tail off. Each stream is narrow, and some wind between obstacles. In such a case, the traditional bends and straights are followed every night. The Naked bats return at the same point they left, and the Lesser Horseshoe causes the only actual streams.
The evening flights of the lesser Horseshoe Bats are one of the daily spectacular, and that of the Naked Bats is less spectacular but can be ever more dramatic. A stream of about 33,000 of the lesser Horseshoe bats passes over the main excavation at the west mouth in less than an hour every evening. The time varied between 44 and 75 minutes before sunset (two every second) and 31 to 63 minutes in November.
The flight of the Naked bats shows even more extreme variations in time and density; on some nights, the whole population goes out and on others, not at all.
Such extreme variability is unique to Niah. On occasional nights, few bats, if any, go out. Many bats are still in the cave until well after dark. There is some definite factor that deters them from flying.
What governs the bats’ movement from the cave? One answer may be the gradual fading of the light. Most bats roost in the bigger chambers where a man can find his way without a torch at mid-day. However, others roost in the true dark zones where night falls unobserved. Still, they fly punctually and more or less together at dusk. At present, the mechanism which causes the bats to fly out is unknown.
Birds and Bats
The total bat population is outnumbered by the bird population, which numbers 1,500,000 breeding adults in the cave. These birds fly like bats in complete darkness. They form direct competition with the bats. From present indications, it appears that 5-6 tons of insects are eaten by these birds.
At Niah, the bird’s nest owners accuse the Naked bat of eating the swiftlets’ nests on the wall. However, there is no evidence that the case is well founded. It seems the only harm the bats do to the birds is to oust them from one cave region to another.
The cave nesting Swiftlets shun the more brightly lit parts of the cave. They seek heights attaching their nests to the upper reaches of any wall right up to the level where the wall meets the cave’s roof. They do not hang their nests to the roof itself. Moreover, at night when the bats are out feeding and by day when most of the birds are out feeding.
There only seems to be competition between naked bats and swiftlets at the cave mouth. The naked bat plunges boldly out of the cave straight into the inpouring swiftlets. The birds duck and twist out of their way as a collision would result in the death of a bird.
Two hawks are common at Niah, the Brahminy Kite and the Bat Hawk and the Malaysian Eagle Owl is often seen. Only the big Naked Bat flies boldly out of the cave of the bats. These raptors feed mainly on the swiftlets.
Man commonly eats only the Naked Bat, but bats are left alone with the onset of Islam among the Malay community. The local sea Dyaks relish the Naked bat’s flesh. They sometimes collect them using lamps or fires in the cave.
From
Lord Medway 300,000 Bats in the Sarawak Museum Journal 1958
BorneoHistory.net
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