Media & Education
BATS Magazine

Volume 12, Issue 4, Winter 1994


By Hall, Leslie S.


WE HAD BEEN traveling upstream by boat past villages and lush jungle for most of the day.
First we navigated the wide and muddy Baram River in a sleek express boat to Marudi, where we transferred to a smaller boat for the next leg of the trip. Finally we boarded a bumboat up the Tutoh River and eventually entered the Melinau River. As we cruised along these liquid brown highways, vividly colored butterflies and birds flashed past the boat.

This was my second trip to the remote Gunung Mulu National Park in northern Sarawak on the island of Borneo. Much of my work on the first trip focused on determining the bat species present, measuring them, recording their echolocation calls for future identification, and making observations on roost and habitat selection. This time, I was accompanied by Lana Little, a Parks and Wildlife ranger from Queensland, Australia. Sarawak's National Parks and Wildlife Section of the Forest Department had asked me to conduct a bat survey of the park. They were especially interested in determining the number of free-tailed bats (Chaerephon plicata*) emerging from the park's caves each night, as well as assessing the status of the highly unusual and vulnerable naked bats (Cheiromeles torquatus). All known colonies of these bats in Sarawak have either greatly declined or disappeared, affording it official protection status.

Borneo is the third largest island in the world, only behind Greenland and New Guinea. It contains a rich diversity of bats, some 100 species. In any given place in Sarawak, bats are the most numerous mammal species. As in other tropical ecosystems, many of Sarawak's bats are essential pollinators and seed dispersers for numerous economically important plants. Products from these include various timbers for commercial harvest, foods, medicinals, and much more. Insect eating bats are also abundant, particularly in the families of Rhinolophidae and Hipposideridae. The elaborate facial configurations and ears of these bats have long fascinated bat biologists who study echolocation.

Gunung Mulu National Park is a lush tropical jungle with fast-flowing streams and jagged limestone outcrops. It is overlooked-by a 7,798-foot mountain and is rich with spectacular and immense caves— some of the world's largest. The massive Gua Payau Cave, with its evening emergence of nearly two million free-tailed bats, is the main feature that attracts adventuresome visitors to the park. There are also many other impressive caves at Mulu, including Lubang
Nasib Bagus, which contains the world's largest underground cavity, Sarawak Chamber, approximately 330 feet high, over 1,300 feet wide, and 2,300 feet long. Another, Clearwater Cave, contains an extensive river system that winds its way underground through over 30 miles of passageways. Despite the park's remoteness, Mulu is becoming one of Sarawak's most popular tourist destinations, and on a busy day up to 60 people may visit.

Although the trip to Mulu is now only 30 minutes by air from Miri, a city on the coast of northern Sarawak, some visitors. still prefer the adventure of traveling by boat through the jungle, which is what we chose to do. As we ventured deeper into the vast rain forest, the rise and fall of the waters was evident by the layers of sediment on the banks; the size of the logs in the flood debris was sobering. Because of the proximity of the warm South China Sea, Sarawak has an annual rainfall ranging from 100 to over 200 inches. But the boat drivers were highly skilled and maneuvered without mishap around whirlpools, floating logs, rapids, and at one point, a runaway timber barge.

It was late in the afternoon when we pulled into Benerat Lodge on the banks of the relatively calm Melinau River, a mile downstream from park headquarters. As the drone of the outboard motor died, we became aware of another sound: a dull continuous hum. The source of the sound soon became obvious as we looked skyward. Snaking and weaving like some magical genie unleashed from a bottle was a large swarm of free-tailed bats twisting across the sky. First one group, then another, and following in succession, yet another. Some spiraled high, others traveled low and fast, but all maintained their long sinuous line. As the evening sky darkened, we watched the bats disappear out of sight to unknown feeding grounds.

Soon after dark, we encountered more bats as several flew through the dining room and darted around the gardens. By using a bat detector and comparing the sounds with recordings of calls I had made in other parts of Sarawak, we were able to recognize Horsfield's myotis (Myotis horsfieldi) and the fawn roundleaf bat (Hipposideros cervinus), one of the most widespread cave-dwelling bats in Borneo. After setting mist nets, we a found short-nosed fruit bats (Cynopterus brachyotis), long-tongued nectar bats (Macroglossus minimus), and a spotted-winged fruit bat (Balionycteris maculata), one of the smallest flying foxes on Borneo at less than half an ounce— all of this, and we hadn't even left the lodge grounds.

DURING THE NIGHT, pink flashes and low rumbles hinted at a storm high in the mountains. In the morning we rose to find that the Melinau had broken its banks. The steps on the river bank, where we had disembarked the day before, were now well below the water's surface. The high water didn't change our plans, however, to reach park headquarters that day and begin our work. In fact, the extra water flowing in the river would make it easier to negotiate the rapids we knew were ahead. We traveled up the river in yet a smaller boat past areas where the swollen river disappeared into the dense jungle.

As we approached park headquarters, the main channel narrowed and became overhung with vegetation Then the jungle gave way to gloomy gray limestone cliffs. Constantly dripping, the cliffs were peppered with cave entrances that were festooned with ferns. We landed in a clearing beside the river. After checking in at headquarters, a guide led us on an elevated walkway into the jungle on our way to Gua Payau Cave or, in English, Deer Cave. It got its name from the Sambar deer (Cervus unicolor) that, in the past, gathered in the entrance.

It was mid afternoon and the forest was alive with sound. As butterflies flitted by, cicadas buzzed and screeched, one species sounding disturbingly like a dentist's drill. Frogs plonked and birds babbled in the upper canopy. Flowers were everywhere. Spectacular orchids hung out of trees, and begonias were jammed between logs and rocks on the forest floor.

A mile or so down the path, we reached a massive rock outcrop with streams flowing out of its base and dark cave entrances everywhere. We had finally arrived at Gua Payau. Swifts dived over the forest, then darted and swerved before plunging into the darkness of the enormous mouth of the cave. We stared up at the gray and yellow overhanging cliffs some 500 feet above us. The jungle reached all the way to the base of the limestone, and large trees jutted out of the cliff.

Gua Payau has two entrances. A distance of 1.2 miles between them makes this the longest cave passage in the world. Inside, the average ceiling height is 250 feet with the passage averaging over 150 feet wide. Because of these factors, only the central area of the cave is in total darkness. A river and a stream also flow through, and other passageways and smaller caves within caves lead off from the main passage.

A concrete walking track has been laid through the cave, making footing a great deal easier for visitors. As we entered, we spotted a green and black cave racer— a snake that feeds mainly on bats. Farther in the cave, just inside the twilight zone, a small creek wound around large boulders before disappearing beneath a wall. Several bats and swallows flew above. The bat detector indicated they were Bornean horseshoe bats (Rhinolophus borneensis), and the audible "feeding buzzes" showed they were actively feeding with the swallows on small insects over the creek. It was only three in the afternoon.

Moving deeper into the cave, we could hear the chatter of more bats. Roosting some 250 feet above our heads, they were in a dark recess in the ceiling. Covering the floor below them were large areas of fresh guano, seething with ravenous cockroaches and earwigs. We identified several dead bats as Chaerephon plicata, the same free-tailed bat whose intriguing hum we had heard the previous afternoon as we arrived. As the trail disappeared into darkness, the clamor of the free-tails was incessant and deafening.

Almost a mile into the cave, a viewing platform signals the end of the main path. Travel beyond this point is not encouraged because the river that runs through the cave here is often swift and dangerous to cross. We, however, had been given permission to continue on to the Garden of Eden, a wonderland of lush and rare jungle plants just outside the northern entrance.

On the way we inspected several recesses in a low ceiling that had tell-tale droppings on the floor beneath. Lesser bent-winged bats (Miniopterus australis), a species we were familiar with in Australia, occupied the hollows. We followed the increasingly poor trail, negotiating a jumble of slippery guano covered rocks and crossing the river which was, fortunately, much lower than flood debris indicated its height could reach. Struggling up the slope, we reached Bat Cave, a cave within a cave, which was full of Cantor's roundleaf bats (Hipposideros galeritus).

Emerging at last from the far entrance of Gua Payau, we entered the Garden of Eden where a myriad of plant species grow in great profusion. Here, another small cave, Porcupine Cave, feeds into Gua Payau. In the twilight zone of this chamber, greater sheath-tailed bats (Emballonura alecto) clung to the wall in their characteristic spider-like manner and deeper inside were more Bornean horseshoe bats. It is not only the sheer size of Gua Payau, but also its configuration, that allows it to shelter so many species of bats. The cave provides a range of roost sites, from large and open chambers to small, warm passageways, accommodating the needs of many different species, both flying foxes and insect-eating bats.

AFTER OUR RETURN to the main entrance, we sat on the veranda of the special bat observation house and waited for the evening event— the emergence of the free-tailed bats. At 5:30, while it was still light, bats swirled just inside the entrance. As more arrived from further inside the cave, they forced the others higher up against the ceiling, and finally they all began to leave.

Long ribbon-like swarms flew low from the entrance. At first, they took 20 seconds to pass, spaced about 10 seconds apart. At the height of the exodus, a continuous stream of bats flowed from the cave. Some groups flew over the jungle for one or two miles and then returned to the entrance where they joined another swarm. Several groups spiraled past the overhanging cliff, forming a doughnut shape high above the cave entrance before breaking into a typical ribbon shape. These groups mostly headed east into the mountains. Others flew high above the entrance and then sped back as though they had to get a better bearing. The most spectacular were the low-flying groups. Weaving like a ribbon in the wind, it was these that produced the intense hum we had heard on our first day, a sound that can be heard for many miles.

We later heard anecdotal reports that swarms of free-tails could still be seen some 20 to 30 miles from Gua Payau.

It took 40 minutes for the free-tails to complete their exodus that evening. Watching on a series of consecutive evenings showed considerable variation in the number of free-tailed bats leaving the cave. One evening, none left. Other counts, based on timed photography, showed over one million emerging. There was no obvious pattern in night-to-night numbers, nor any significance in the presence or absence of storms. The night we calculated the maximum number of 1.8 million bats leaving, there were still many left inside the cave.

Activity didn't end as the last free-tails departed into the jungle. There were yet more bat species to leave the cave. High-pitched squeaks from amongst the moss-covered rocks near the entrance came from several young Philippine horseshoe bats (R. philippinensis), which appeared to be unable to fly and were likely accidentally dropped as their mothers left to feed. Cave nectar bats (Eonycteris spelaea) flew swiftly along the walkway and then sped off through the dense jungle. Remarkably, they navigate by eyesight alone through a nearly lightless cave and then through the jumble of vegetation below the forest canopy, even on cloudy nights. Although their guano contains mainly pollen, germinated seeds from rain forest trees can often be found as ghostly pale plants sprouting under their roosts.

High above the canopy we at last saw several naked bats leaving the cave. Cheiromeles torquatus is one of the world's largest insect-eating bats, weighing up to 160 grams (almost six ounces), with a forearm of 180 mm (about seven inches), a size more typical of a flying fox. They are almost completely devoid of fur, making them look as if they are wearing an oversized leather jacket. Against the fading sky, the last swiftlets returning to the cave gave the large silhouettes of the departing naked bats a wide berth.

Another storm approached as the last bats exited the cave. Soon after we headed back to park headquarters, the heavens opened with rain so heavy that our umbrellas were useless. But about halfway back, the downpour stopped and the beauty of the rain forest night revealed itself. Fireflies played tricks with our eyes, and small colonies of fungi covered dead leaves, creating a luminous fairyland on the jungle floor. Cicadas buzzed, owls hooted, and geckos barked, while a chorus of frogs provided background music. After rain, an astounding variety of insects appeared on the walkway-an entomologist's dream. Bats darted along and across our path, as if leading the way

In one day we had encountered 14 species. The number recorded from inside Gua Payau is 12, and it is likely that another six species will be added to the list. The only recorded Borneo specimen of the tail-less roundleaf bat (Coelops robinsoni) was a dead bat picked up on the walkway in Gua Payau. The colony of naked bats at Mulu is very small, perhaps less than 50 individuals. Fortunately their roost is in an inaccessible upper section of the cave and safe from human disturbance. More observations are needed to ensure the long-term survival of naked bats at Mulu.

It is fitting that such an impressive cave is the home of so many different bats. My work in Sarawak is not over; very little is known about the countries bats, and much remains to be discovered. Sarawak is becoming very interested in promoting ecotourism, and since their many bats are part of the attraction, they naturally want to learn more about them. As more people visit because they want to see spectacular sites like Gua Payau Cave, Sarawak will have good reason to take care of its rich bat fauna.

GUA PAYAU, with 12 bat species recorded, may hold the world record for number of species found in a single cave:
1. Cave nectar bat, Eonycteris spelaea
2. Greater sheath-tailed bat, Emballonura alecto
3. Bornean horseshoe bat, Rhinolophus borneensis
4. Philippine horseshoe bat, R. philippinensis
5. Cantor's roundleaf bat, Hipposideros galeritus
6. Fawn roundleaf bat, H. cervinus
7. Dayak roundleaf bat, H. dyacorum
8. Diadem roundleaf bat, H. diadema
9. Lesser tail-less roundleaf bat, Coelops robinsoni
10. Lesser bentwing bat, Miniopterus australis
11. Naked bat, Cheiromeles torquatus
12. Free-tail or wrinkle-lipped bat, Chaerephon plicata

Other bats recorded in Gunung Mulu National Park and which may yet be discovered in Gua Payau:

1. Dusky fruit bat, Penthetor lucasi
2. Spotted-winged fruit bat, Balionycteris maculata
3. Creagh's horseshoe bat, Rhinolophus creaghi
4. Bicolored roundleaf bat, Hipposideros bicolor
5. Horsfield's myotis, Myotis horsfieldi
6. Black myotis, Myotis ater

Leslie S. Hall is a Senior Lecturer in Anatomical Sciences at the University of Queensland, Brisbane, Australia. He is a member of BCI's Scientific Advisory Board.

(Footnote 1)
>* Formerly Tadarida plicata.

Cave nectar bats form large colonies on the roof of the cave.Their guano contains mainly pollen, such as from this wild banana, but germinated seeds from rain forest trees are also found sprouting beneath their roosts in Gua Payau.

A wide variety of bats, from insect eaters to nectar- and fruit-eaters, live in the rainforests of Mulu. Seeing free-tailed bats emerging from the huge entrance to Gua Payau (opposite page, top) is one of the highlights of a visit to the park. Visitors might also catch a glimpse of the tiny spotted-winged fruit bat (opposite page, bottom). Weighing less than half an ounce, it is one of the smallest fruit bats in Borneo. Bornean horseshoe bats (top) are widespread in the many caves of the park. Bicolored roundleaf bats (bottom) are found throughout Mulu and may yet be discovered roosting in Gua Payau.

Short-nosed fruit bats are common on the grounds of the lodge just outside of Mulu. Their seed dispersal and pollination activities are critical to the propagation of rainforests.

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