Niah National Park Background – Ecology of the Caves


As well as being spectacular, the caves at Niah have a unique ecology. Unlike the rainforest outside, where the whole system is driven by the sun, the ecology of the caves is fuelled by another energy source – guano (bird and bat droppings). Millions of swifts and bats have made their home in Niah’s Great Cave, for countless eons. They feed on insects in and above the rainforest (swifts during the day, bats during the night), then return home to rest, digest, and poop. Although the individual droppings are small, by sheer weight of numbers, huge volumes of guano are deposited in the cave – in some places it is more than 9 metres deep!

All this guano is a food source for a host of insects, as well as unique creatures which feed on the insects or the bats and birds themselves. Many of these insects and animals never leave the cave, and have evolved to survive in the dark – all forming part of a complex self-contained food chain, only linked to the outside world via the bats and birds.

The most obvious and common of the cave inhabitants are the cockroaches and earwigs, which feed on the guano. In places, they practically swarm on it, but usually there are just a few. But there are other amazing denizens of the darker recesses which you may meet, if you are lucky.

Unique cave creatures

Giant carniverous crickets

Giant carnivorous crickets
Giant carnivorous crickets

One of these is the giant cave cricket (Rhacophota oophaga), which is often seen in the darker parts of the cave, especially the area between Lobang Bulan (Moon Cave) and Lobang Gan Kira (the exit towards the painted cave). Although they look much like ordinary crickets, they are huge – their bodies up to about 6 cm , and antennae up to 15 cm. These crickets also have one other distinguishing trait – they are carnivorous and eat swift eggs (hence their scientific name – oophaga means ‘egg-eating’).

Long-legged centipedes

If you are extremely lucky, you might see a long-legged cave centipede (Scutigera sp). These extraordinary creatures have incredibly long, thin legs – out of all proportion with their bodies – and look like nothing else on this earth. (In case you miss it in the cave, there is one preserved in perspex in the National Park’s information centre.) In 1961, Tom Harrisson noted that these “extraordinarily nasty long-legged centipede[s]” are not unique to Niah, but are confined to a few caves over a wider area.

Invisible geckos

Feeding on the cockroaches, and possibly other small insects and even fallen baby birds, is the Niah cave gecko (Cyrtodactius cavenicolus). This gecko is known only from parts of Niah Cave, and is not found anywhere else in the world. However it is a dark colour, very shy, and lives in “the ultimate dark of guano-depths” (Harrisson again). It is also reputed to be able to move incredibly fast – faster than the skinks you see on the boardwalk, or the small geckos sharing the national park accommodation with you. Also unlike other geckos, the Niah geckos are silent and do not make any calls. These traits all mean that you would have to be very lucky to see one.

Cave-climbing snakes

Cave-climbing snakes
Cave-climbing snakes

Another cave reptile, which feeds on bats swifts and swift eggs, is the cave racer (Elaphe taeniura). This snake is capable of climbing high up the steep cave walls, to reach its prey. (Don’t worry, they’re not known to drop down onto unsuspecting humans, and are pretty rare.)

Bats, Birds and Birds Nests

Finally, there are the bats and swiftlets themselves, on which all these other animals are dependant.


Sarawak Bats

About six species of bats live in the caves. The most common of these by far are small Cantor’s roundleaf bats (Hipposideros galeritus). Naked bats (Cheiromeles torquatus) can also easily be picked out in the evenings as they leave the cave – they are much larger than the other bats, and their wings make a loud swooshing sound. Watching the bats pour out of the cave at dusk is quite an experience (although they are not in the same numbers as at Mulu’s Deer Cave, nor do they fly out in spiralling formations). You also have to be careful with the timing – the ferry boatmen on the Niah River back to the Park HQ often pack up and go home between 7 and 7:30pm.

Surprisingly little is known about the bats, their diets or habits – it was not even known until recently what part of the cave the naked bats live in. Their guano is now being studied for the first time, to determine their diet. Roosting patterns of the naked bats are also being studied, to try to determine how regularly they leave the cave, and why they sometimes stay in it for several days without leaving.


The birds in the cave are primarily the black-nest swiftlet (Collocallia maxima – the name Aerodramus is also sometimes used for the swiftlet genus) and the mossy-nest swiftlet (C. vanikorensis). Like bats, the swiftlets use echolocation to find their way in the dark of the caves – and to locate their insect prey. The constant clicking sound can easily be heard in the caves – at times more of a buzz than clicks.


Birds Nest

Sarawak Birds
Sarawak Birds

It is no coincidence that these birds have been named for their nests. These little nests, made from a special type of saliva, are the highly prized and extremely valuable chief ingredient in birds’ nest soup (1kg of nest may fetch in excess of US$1,000!). Birds’ nest soup is a Chinese delicacy, regarded as highly as caviar in the west – and not much more bizarre, if you think about it.

Niah’s fame stems in part from these nests, which are collected by men shimmying up incredibly high and precarious-looking poles, to scrape the nests from the cave ceiling, in places more than 40m (15 stories) high. Writing in 1947, Tom Harrisson recorded that ‘It is frightening even to watch a man ascend these slender poles. Every now and then, someone falls and is killed.’ It is still a dangerous business today.

The tangle of poles in the cave is extraordinary, and witnessing the collecting season is a sight to behold – the cave is lit up as if with fairy lights, as collectors search for nests in the high, far reaches of the huge cave. Some of them will stay up there for as long as a week; and as many as 200 people may be living in the cave at any one time.

The birds’ nest collecting has been going on at Niah for centuries – possibly since the 8th century, judging from the age of some of the Chinese pottery shards found in the cave. By the 1880s, tax on birds’ nest was Sarawak’s fourth largest source of revenue, and it continues to be commercially important today.

The primary focus for birds’ nest collection at Niah is the nest of the black-nest swiftlets. These nests have some twigs and feathers mixed-in (hence the name), which requires them to be washed and cleaned, and the feathers and dirt removed by hand, before they can be sold. The mossy nest swiftlets’ nests are not edible and thus not commercially valuable – the birds mix-in too much moss and various other things with their nests, making them unusable.

Guano again

Birds’ nests are not the only commercial resource collected from Niah. The huge piles of guano themselves have also been a source of income for generations of guano-collectors since the 1930s. The guano can be used as a fertiliser, and was important during the pepper-boom of the 1930s. The collection of guano is now only done by a few individuals, partly because actual digging has now been prohibited (to protect the cave’s delicate environment and important archaeological sites), but mainly because synthetic fertilisers are now more effective and more readily available. However, there is still some demand for guano, because of its effectiveness in also preventing root-rot in pepper vines – still a major regional cash-crop. Guano is now collected only by sweeping-up fresh droppings. The guano is put into large sacks, probably weighing a good 30 kg or more. These massive sacks are then carried by foot all the way along the boardwalk to Pankalan Lobang (about 4km), from where they are loaded into boats. In fact, the boardwalk and Pangkalan Lobang (the trading house at the river) were originally built to make life easier for the guano-carriers.

Population declines

Unfortunately, all this human activity has had a major impact on the delicate web of life within Niah’s caves. In the late 1950s, when they were calculated for the first time, the swiftlet populations in Niah’s Great Cave complex were estimated at over 1.5 million, and the total bat numbers in excess of 300,000. (Now you can understand how all that guano got there!) However, recent estimates of the swiftlet numbers placed them at possibly as low as 150,000, with the bat populations having shown a similar marked decline (although possibly fluctuating significantly as well). Presumably there have been flow-on impacts on the populations of other cave species which are dependent on the birds and bats.

There are thought to be a number of reasons for these dramatic declines. The most obvious, and probably the most significant, is the over-collection of nests. Nest collectors are under intense commercial pressure, and the value of the nests also makes them a prime target for poachers. But there are probably other factors as well – the clearing of forests to make way for palm plantations, and the use of commercial insecticides are both likely to have impacted the insect populations which form the diet for both bats and birds. Further, studies have shown alarming levels of insecticide residues in the swiftlets themselves.

Major efforts are now being made to reverse the trend. The government, quite sensibly, has recognised that it would be unfair, and near-impossible, to simply ban outright the centuries-old and extremely lucrative nest-collection (it would just push it ‘underground’ – so to speak). So the government is making efforts to work with all stakeholders in the Niah region, to try to ensure the sustainability of the practice, and to reduce other external pressures on the populations. Several large community and stakeholder meetings have now been held at Niah (‘the Niah Gatherings’), to develop measures which include, and are acceptable to, all stakeholders. Such measures have included closed seasons on nest collecting, to allow undisturbed nest re-building. Initial signs are that the agreed processes may be starting to work, with swiftlet numbers slightly increasing in recent years. However, it will still be a long and difficult process. (Another proposal is to breed swifts in ‘artificial caves’ – in empty houses and purpose-built buildings – to help take the pressure off wild swift-nests.)

You can do your bit to help by ensuring you don’t throw any rubbish in the cave. You could also hire a local guide, and buy drinks and (non-wildlife) souvenirs from the locals – the more benefits they see from tourism, the more concerned they will be with preserving the integrity and sustainability of the national park.