Tunnels to a Wildlife Underworld
Acutely sensitive to human presence, the bats can quickly become airborne, turning a calm cave into what feels like a giant wind tunnel. Darting through their tubular home, the tiny creatures emit high-pitched tones: an ultrasonic symphony that forms the basis of their echolocation systems. Thanks to their vast numbers, bats are a key link in the fascinating biological cycle which has evolved around Undara’s equally remarkable lava tubes.
The story beings about 190,000 years ago when volcanic activity was shaping and re-shaping this part of northern Queensland. Undara, the region’s second youngest volcano, was funnelling enormous volumes of molten rock out onto the Atherton Tablelands. Gently sloping plaints were flooded in places by an estimated 23 billion cubic metres of lava. It oozed, at initial temperatures of between 1,175°C and 1, 220°C, across 1, 550 square kilometres of land. Researchers studying the depth, width and distance travelled estimate that Undara’s geological cocktail spewed forth at about 1,000 cubic metres per second – enough to fill 1,500 semitrailer-sized tankers every minute.
This incredible volume along with the terrain, not too steep and not too flat, allowed the lava to flow at a rate conducive to tube formation. Where is filled an existing depression (probably a watercourse), the flow gradually formed a tube. Its surface, in contact with cool air, solidified. Now like a thick, insulated underground river the lava beneath forged a path downstream, the longest arm finally extending 160 kilometres north-west.
Once Undara’s eruption ceased, the insulated lava drained away, leaving a 100-kilometre-long pipeline. Hundreds of thousands of years have seen weaker sections of the tube collapse to form today’s line of depressions and caves. It is this remarkable lava-cast environment in which bats have triumphed.
“Thanks to their sheer numbers, bats have a major influence on life inside and around the caves. During the wet season they gather in vast nursery colonies to raise their young,” said tour guide Val Speedie, who spent a week showing me the many and varied formations that have stemmed from Undara’s rage.
When they breed, three major nursery caves, usually open to the public, are closed. District ranger Lana Little describes this as sound management practice that will help ensure young bats can be raised without disturbance. “We are currently observing bat behaviour in an effort to work out their maternity cycle,” she said. By the end of March the cycle appears to be complete and tourists can safely return to these restricted areas.
The policy recognises how important bats are to the unique biological system that has developed around Undara’s tubes. There are four main insect-eating species, including small cave eptesicus Vespadelus troughtoni, eastern horseshoe Rhinolophus megaphyllus and two species of bent-wing Miniopterus schreibersii and M. australis.
Not only do the form an important part of the food chain – as insect predators and bite-sized meals for snakes and birds of prey – they also have a significant effect on cave atmosphere. Bat droppings or guano can build thickly on the tube floor, often supporting fields of fluffy white fungi. The guano provides a source of food for cave animals and, as it breaks down, produces ammonia and carbon dioxide. Depending on a cave’s physical shape and size of its entrance these gases have a profound influence on life inside.
Collapsed sections of tube, marked by remnant rainforest patches, often mark the start of a tunnel. Describing the enormous variety of cave entrances, Val Speedie said: “You can sometimes find yourself crawling through ridiculously small passages that are very hard to get through. Often, the larger the opening the shorter the tube. The biggest and most spectacular caves tend to have small, almost inconsequential entrances.”
Bayliss Cave, the longest single tube in the Undara system, is a typical example. For biologists and geologists, the cavern could be described as a small patch of underground heaven. But sliding between large beach ball-sized boulders, down a narrow shaft into a pungent and pitch-black chamber, the access feels more like a passage to hell. Inside, atmospheric conditions are uncomfortable. Temperatures inside Bayliss usually hover around 22°C, with humidity levels that can rise above 90 per cent. The stale air reeks of bat guano, and hanging from the ceiling, fibrous tree roots drip with condensation.
Extending at least 1,350 metres (surveyors have yet to go further) Bayliss Cave is up to 11.5 metres high and 18.9 metres wide. While every tube provides crucial habitat for cave-dwelling animals, Bayliss is generally considered one of the most biologically important. Its claustrophobic opening and enormous length have helped to create extremely poor atmospheric conditions when compared to the world outside. Aptly described by scientists as a “bad air cave”, carbon dioxide levels have been measured at 5.9 per cent – almost 200 times the normal concentration found in air. Due to this atmospheric factor, the difficult entrance and significant biology, public access is prohibited.
To move deep with Bayliss Cave without breathing apparatus is a dangerous activity. At floor level, where heavier-than-air carbon dioxide collects, it can be impossible to light a match. But what is unhealthy for we surface dwellers isn’t necessarily bad for cave fauna. In fact Bayliss features such an abundance of life, dominated by things that creep and crawl, it would well feature in an Indiana Jones Hollywood adventure.
The floor is covered with tiny creatures: silverfish-like Isopods, white cockroaches and weird Scutigerids. The latter are bizarre cave-dwellers reported to grow up to 10 centimetres long. With perfect control Scutigerids shuffle each leg forward, one after the other, creating a synchronised ripple effect, much like millipedes. Scutigerids, like most of the other cave-dwellers around them, have no pigment. Living in complete darkness they don’t need to hide behind a coloured camouflage and, similarly, they don’t need eyesight.
Entomologist Frank Howarth, from the Bishop Museum in Hawaii, found the deeper passages of Bayliss contained up to 200 times the ambient atmospheric level of carbon dioxide and a water-saturated atmosphere. Yet he has discovered the most diverse community of highly modified, terrestrial cave-adapted species yet known. Howarth believes the Undara system is one of the most important cave sites in Australia and certainly ranks as one of the world’s best biological caves. “I can’t property describe it without waxing into hyperbole,” he wrote in a recent letter.
“There are between 35 and 40 cave-dwelling species now known from the Undara lava tubes. There are probably a few more in collections that haven’t been identified yet, and many more species from lesser known caves still to be collected. We also have perhaps 100 new cave and surface species from the area that are not obligate cave-dwellers. Only a dozen or so of these have been described to date.”
Howarth also suggests that further research into how cave species have adapted to stressful gas concentrations, like those found in Bayliss, could greatly improve our understanding of the physiology of respiration. He compares this idea with desert animals and how studies into them have helped us understand the ways in which such species deal with water loss. “You can’t do the studies on normal critters, often because the adaptations might be confused with other uses, so physiologists look for organisms specialised for the extreme of what they want to study,” he said.
For many years the Undara tubes, like lava tubes worldwide, attracted little scientific interest. All that changed when NASA scientists began hypothesising that river-like formations on the moon may have been formed by lava flows. The snaking channels couldn’t have come from water as the moon lacks atmosphere. Collapsed lava tubes, and flows that have formed long ridges, therefore gained popularity as possible explanations.
The NASA observations turned scientific attention towards tubes on Earth. Basalt areas were extensively searched to find analogous terrestrial formations and in 1972, at a NASA-sponsored conference on lava tubes, a surprise but critical break-through occurred. Atherton Tablelands resident and geologist Anne Atkinson approached on the space agency’s scientists with pictures of Undara’s lava formations. Her photographs turned on to be exactly what NASA was looking for.
“I had taken a few pictures of a feature called The Wall and thought it looked similar to a picture of basalt areas on the moon in an old National Geographic,” recalled Anne. “So, as shy as I was after 25 years in the bush, during lunch I inched over to the NASA man Ronald Greeley and said would you come and have a look at a few pictures from Australia. When he saw them he was just so thrilled. He said of all the air photos they had examined nothing had come up nearly as good as the Wall.”
Anne, who by chance began studying the Undara system in 1972, says Greeley’s response was one of the most exciting moments in her life. She had earlier been diagnosed with cancer and, given only months to live, Anne’s doctor suggested she find an outside interest to occupy her time. That’s when an opportunity to survey the Undara tube system arose.
The contact with Ronald Greeley, she reckons, was the cancer cure. “I was invited to NASA which was a great experience. Then, when I came home it was a bit hard to be really concerned about the housekeeping and gardening. I found everyone had lived quite well on vitamin C tablets, so I’m afraid I got more and more involved with geology.”
Whether from the air or at ground level, tube collapses are easy to spot. Dark green, densely vegetated areas signify vine thicket that grows wither inside a tube collapse or on one of many “lava ponds” that have formed around the main tube line. They stand out dramatically from the more typical eucalypt savanna growing on red earth. Moving between the two vegetation types is like crossing between two radically different worlds.
During the wet season in particular, walking through the savanna can be hard work. Sparse tree cover affords little shelter from northern Queensland’s intense tropical sun. Small eucalypts are surrounded by grasses which during a good season grow about one metre high. Along with outer edges of vine thicket bottle trees Brachychiton australis, similar to Western Australia’s water holding boab, stand like giant sentries. Step beyond them and the ground is strewn with basalt boulders that are riddled with tiny holes.
With the rocky ground acting as fire retardant in otherwise fire-prone country, today’s vine thicket has survived from an age when lush forests were normal in this part of Australia. Resident wildlife, like the unadorned rock wallaby Petrogale inornata also helps keep fire out. They graze along the vine thicket margins, placing even more distance between flammable grasses and their sensitive remnant rainforest home.
Inside each tube collapse the air is damp and cool. At the base of a typical depression likes a world of moss-covered rocks, fig tree trunks and tangled rainforest vines. After rain, ornate fungi pops up everywhere and huge millipedes emerge from the rich leaf litter. These well-armoured animals are about 12 centimetres long and about one centimetre in diameter. Touch them, and in defence they shoot out a brown liquid that burns like acid.
Similarly, ornate pythons rely on the tube environment for survival, with bats forming an important part of their diet. In an intriguing display, children’s pythons Liasis childreni venture inside the tubes, climb its walls and hunt their prey from the ceiling. Even more spectacularly, they sometimes hang in trees just outside the small entrance at Barkers Cave. Competing for position with eastern brown tree snakes Boiga irregularis, the two tree-climbers snap at bats that swarm from the cave at dusk. With tens of thousands flying past, the snakes just keep on lunging. Occasionally they manage to pull a bat from flight and, in an instant, wrap themselves into a constrictive coil.
Death is quick and soon the complicated process of consuming an animal with long, bony wings begins. An unpleasant end for the bat perhaps, but it’s another small link in the remarkable chain of life that revolves around Undara’s tube formations.
Undara Volcanic National Park, one of Queensland’s newest conservation areas, has the potential to be one of the most visited sites in north-western Queensland. Due to its sensitivity, however, Queensland’s Department of Environment and Heritage (DEH) has decided to allow only supervised public access.
Anyone who wants to visit the lava tubes must do so with a Savannah Guide from The Undara Experience, the company with exclusive rights to conduct tube tours. In addition to guiding services, The Undara Experience also operates a comfortable lodge and camping area on land just outside the park.
Owned and operated by the Collins family, cattle farmers on the Atherton Tablelands since 1862, they negotiated the management agreement with DEH as part of a land acquisition deal in 1992.
Gerry Collins, who runs the concern on behalf of his family’s trust company, said he spent 25 yeas working the neighbouring cattle station Rosella. Since childhood he had always known of the tubes’ existence, but it wasn’t until the 1980s that he decided there could be a future in combining tubes, cattle and tourism.
“We bought the property with the crater and about half of the lava tubes in 1989. Our idea was to run a tourist operation in conjunction with a small number of cattle,” said Gerry. “Then in 1991 the Environment Department expressed their interest in acquiring the land.”
Although Gerry wasn’t too pleased about the idea of a government body moving in and forcefully taking his family’s property, he was able to negotiate an agreement which today appears to be working well for both sides.
At present a quota, set by DEH officers, allows 200 people per day to visit the tubes. About 20,000 go on tour each year and the quota is regularly met during the busy dry season. While this system provides considerably more security than if people were allowed to wander through of their own accord.
Acknowledging these concerns, district ranger Lana Little said her department would like to see the introduction of a budget tour once the current daily quota can be lifted. “People are finding the fee structure restrictive, especially if they have a number of kids,” she said. “We plan to develop walkways that will reduce to almost zero the impact on the vine thicket floor and the caves themselves.
“We also have plans to install information signs in parking areas, to improve the roads and to provide disabled access.” When complete, Lana said it will be possible to allow more people in the park.
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