Going batty in Sarawak's Gunung Mulu

Published December 4th, 2013

There's something pretty cool about watching three million bats emerge from a cave, spin around in formation and jet off into the distance in search of a hearty dinner.


Yep that's right, you read correctly - three million little critters.


But these bats aren't your usual run-of-the-mill fruit bat variety that inhabit Sydney's botanic garden or fly over the roofs of the North Shore each evening. I was watching the so called micro bats of the Gunung Mulu National Park, a UNESCO heritage listed region that's only accessible by air - situated deep in the Malaysian Borneo jungle. These rather cute nocturnal marsupials wake like clockwork around 5.30 each evening after a full day of hanging about rather precariously to the ceiling of the Deer Cave.


 The entrance to the Deer Cave


Before the mass exodus of epic proportions, John, my guide with the tour company Planet Borneo, offered to show me inside the cave.


We walked for around an hour from the park headquarters along a boardwalk – passing a juvenile pit viper, which if it bit me I probably wouldn’t have the ability to tell this tale. Pit vipers are particularly deadly but the juvenile even more so because they don’t have much self control – they just keep injecting poison.


I kept my distance from the viper and approached the entrance to the Deer Cave.


I was expecting to see the ceiling covered in bats – after all it would take a lot of real estate to accommodate three million bats. But nothing in Mulu is as it seems – especially when the Deer Cave has the largest cave passage in the world. The three million bats were completely absorbed into this vast cavernous expanse. In Mulu size really does matter – apparently it’s because of the massive volume of water that falls onto the limestone; this is a rainforest after all. This limestone is rather spec also – it’s very fine-grained and super tough, making the cave resistant to collapse.


This cave is one of four show caves in the national park - the Lang, Clearwater and Wind Caves round out the quartet and was named after a deer that was spotted in the entrance.


While naming rights went to Bambi, the resident bat population were indirectly responsible. The precious salt that the Deer was in search of is found in guano – which is more commonly known as bat poo. Yeah – it sounds totally gross but three million bats generates some serious poo. Great swathes of the cave floor are covered in the stuff – from a distance it looks like a barren desert of black earth. But on closer inspection, there is an entire ecosystem of insects having the time of their lives scurrying and digging into the bat poo.


 Inside the Deer Cave


While it’s fascinating to watch beetles – I was here for the caves and the bats.


Guide John shines his torch into a cylindrical hole just above our head.


"There they are," he exclaims.


I look up to have four sets of adorable bedroom eyes look down on me. These micro bats are no bigger than my fist. Their faces are incredibly cute and have an unmistakable expression that says, "Stop shining a torch into my face and let me go back to sleep because I need all my strength and energy to fly throughout the night."


I admire the little treasures for a moment longer before proceeding deeper into the cave.


 Micro-bats resting


Thirty bat species call the Gunung Mulu home – of which 18 micro bat species live in the caves. Deer Cave shelters at least 12 of these species, which is the highest number of bat species occupying a single cave that’s ever been recorded. These micro bats can be divided into two groups – those that eat insects and those that devour fruit. John says that it’s easy to tell the difference between the two because the insect-eating bats are ugly. The real difference is in their eyes.


We continue to wander through the cave system admiring the various formations and being in absolute awe of the sheer size of this cavern. But really – it’s all about the bats – so I was keen to wind up the sight-seeing and make my way to the viewing point.


I take pride of place on the benches and wait. On some nights when the rainfall is too intense the bats don't parade for the tourists. It isn't so much the fear of getting wet that deters them but rather their ability to zero in on unsuspecting prey is severely affected. Bats have this fascinating way of spotting insects through a process known as echolocation.


Luckily for me, my prayers were answered, and the clouds stayed away. All that's required from me is patience. While it’s an affirmative that the bats will appear - the precise time is never a certainty.


John tells me that the bats won't appear until the direct sunlight on the entrance to the cave has subsided. Bats after all are afraid of sun light.


I don't quite know what I was expecting. I knew there would be three million bats. I suppose I thought that all of sudden I'd hear this whosh of sound - and then I'd see millions and millions of bats flying in a mad flurry of activity ravenous to feast on the first available unsuspecting tasty morsels.


 Serpent-like formation


But to my utter amazement - it wasn't some chaotic free-for-all with bats flying everywhere helter skelter. And the bats didn't emerge all at once but in groups.


Each group flew in perfect precision that would make the royal air force envious.


The first colony soared up the cliff face and glided through the air in a serpent like fashion - curving through the dusk sky as one long train until they disappeared into the distance.


The next group resembled something of a phoenix, rising majestically into the sky with a long body and two wings on either side. Another serpent formation – even bigger than the first - followed closely behind.


 Another formation


I was transfixed. It was almost as if these bats had been practising inside the cave and were performing for the tourists.


The show lasted for around 30 minutes. There were about 15 groups in total - so that's about 200,000 bats in each group.


Where they fly and how far they travel is anyone’s guess. They might cross the nearby border into Brunei, because much of Brunei's forest region remains intact.


"No passport, no problem," John jokes.


John tells me that the bats will return to the Deer Cave at about 4.30 tomorrow morning. They will come home to rest individually after they've eaten around ten grams of insects each – this is the reason why mosquito bites are rare in Mulu – because the bats eat the mosquitoes. Finally there’s a rainforest that you don’t need aeroguard.


The return walk back to the park’s accommodation options is a humbling affair. I remain speechless, confident that I’ve just witnessed nature at its most awesome.