Life in the batcave

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Flies, cockroaches, beetles, crickets and millipedes live according to their preference in either the wet or dry bat guano and lie at the lowest level of the ecosystem being coprophages or dung eaters.

Preying upon these guano feeders; pseudoscorpions and centipedes stalk their prey in the smelly gloom.  Egg-eating crickets feed on swiftlet eggs and chicks and are well big enough to be alarming if one jumps on to you in the dark.

Larger predators are about, and cave racer snakes up to three metres long are excellent climbers and will seek out swiftlet nests and fallen baby or dying bats.  These snakes are also found outside in the rainforest canopy. A large specimen hunting on the dry guano allowed us to approach closely, like everything else in the cave system, including us, he is covered with flakes of dry bat guano.

Counting and identifying bats
It is difficult to accurately estimate numbers of bats in large colonies.  Scientists use a number of methods but the easiest is to use a camera to photograph the emerging stream of bats at regular intervals from the same viewpoint (this ensures that the shots are all from the same distance), and of different widths of bat flow. Then calculate how long it takes a single bat to cross the viewfinder.   Once you know that, and assuming that the bats fly at a constant speed, which they do, you can count in the photograph, the width (in numbers of bats) of the stream and end up with a calculation of the number of bats per second leaving the cave.  Of course its wise to pick a night of fine weather because much fewer bats leave the cave when it is raining, as their insect prey are largely grounded, and the bats may have difficulty flying with a waterlogged coat.

Identifying the particular bat species is simpler, each species has a unique echolocation signature that can be picked up using a bat detector, a small receiver with a directional aerial.  Match the frequency of sonar emission to the species and you've got your bat.

Biospeleology - the buzz words
Biospeleology is the study of underground biology and the environment,

Trogloxenes are creatures that live and breed inside caves but feed elsewhere.  These are the bats and the swiftlets which bring the energy into the cave system.

Troglophiles are creatures that can live inside the caves but are also found outside eg the cave racer snakes, Bornean horned frogs.  They are attracted by the food sources in the cave and may live there permanently but the point is that they don't have to.

Troglobites  are the permanent residents of the cave ecosystem and cannot survive in the outside world, usually because they require the high humidity environment and constant temperatures inside the cave.  Many of the insects are troglobites and have adapted to cave life in the dark humidity. 

Caves and living fossils
Throughout the life of the planet most parts of the surface have undergone frequent climatic changes and upheavals eg  mountains now, may have been former seabeds.  The tropics have alternating between savannah and rainforest for recent geological time, as warm and glacial periods in the northern hemisphere influence the tropics,  and deliver dry and wet weather cycles there.

The Bornean rainforest is unusual in that due to its location it has remained as undisturbed rainforest for the past several million years when much of the other tropical rainforest reverted to savannah grasslands because of lack of rainfall.  This stability has led to the area being recognised as a one of the world's centres of biodiversity as a result of much lower rates of extinction than in other more climatically disturbed parts of the planet.

Cave systems in Sarawak, like Deer cave, have experienced stable environments for geological time and the troglobites that live there have had the long uninterrupted time needed to develop their specialised adaptations to life in a dark but very humid environment. 

Adapted to living in the dark
Bats use echolocation to navigate in the dark and to find food.  Echolocating bats send out pulses of high frequency sound that we cannot hear.  By measuring the time between the sound leaving itself and returning as a echo to its ears, a bat can work out how far it is from an object like the walls of its cave home.  Changing intensity and pitch of the returning sound echo give the bat information about its target, eg whether it is a moth or a mosquito.  Some call through their noses, others through their mouths, but amazingly both types can eat and echolocate at the same time.

It's not only the bats that can echolocate, the swiftlets produce sonic pulses by clicking their tongues so that they can find their way to their cave roosts.

Phil Chapman, a biospeleologist who has worked in Deer Cave told me, 'There are blind pseudoscorpions living in Deer Cave that not only have unusually long claws and legs but have also developed long hairs on their body which are able to pick up air currents made by their prey moving about nearby.' 

'Some cave pools contain crustaceans that are living fossils which have been around since all the earth's continents were one - Pangaea, and that's a long time ago.'

Many of the insects exhibit special adaptations to life in the dark, such as the extremely long antennae seen on the centipedes and crickets, and the long legs on the spiders and centipedes.  Huntsman spiders, at the pinnacle of the invertebrate food chain, rely on the detection of vibration to locate their prey  then inject venom which kills their cricket prey in seconds.  Some specimens grow as big as a human hand. 

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