A Natural History of Australian Bats: Working the Night Shift

Chapter 1: Introduction

To hold a little microbat in your hand, its body the size of the end of your thumb, is nothing but astounding. Its head is nearly the size of a man’s fingernail, its tiny ears are twitching as it struggles to get free, its eyes are on you, and then it bares its teeth to try and scare you into letting it go. Inside that tiny head is a powerhouse of information. Some of our little bats know the entire landscape of our east coast, and can pinpoint a cave entrance in dense forest 500 km from its last home. When it gets there it knows what to do – where to forage, which bat to mate with and how to avoid local predators. Through sound it can work out which obstacles to dodge and which insects to eat – and, when it does find a suitable insect prey, it can do better aerobatics than the best aircraft pilot to catch it. The bat is not aware of this, but as it does its thing to survive each day, it is unknowingly providing services to mankind that are so huge that without microbats the world would be totally different. It would be a place so intolerable that our lives would be worse than if we lived in a mangrove swamp full of mosquitoes and other biting creatures and where pest insects would eat most of our agricultural produce. As you will discover in this book, our fascination with bats is only exceeded by our respect and admiration for them.

Take any night when we may be out catching flying-foxes for some particular research project, such as releasing them wearing a transmitter. We would have set our nets near flowering or fruiting trees, because we know that some will eventually visit through the night. Getting a 1 kg flying-fox out of a net is a huge adrenalin rush, but eventually it is subdued and into a cloth bag. Like a microbat, it is a total package of knowledge and experience. It may be 20 years old, and would have visited more places in Australia than a human citizen of the same age. You look into its face; big eyes look back apprehensively. (Once weighed, measured and banded, it is set free.) When it is first captured, it is covered in pollen, or it may have fragments of rainforest fruit in its teeth. If we caught it in Melbourne then it could well have been in Lismore the previous week. It knows where all the eucalypt blossom is located along the east coast, and can smell when the trees are flowering. Through its services to humans it would have pollinated thousands of eucalypt trees that year, thereby creating seeds that eventually grow into trees. In its lifetime it has probably helped tens of thousands of trees to make seedlings. The timber in your house may well have been the result of flying-fox services 50 years ago. But it is now not in Melbourne just to pollinate trees, no, sex is on its mind. It will live in a colony with others that are also better tourists than many Grey Nomads. If it is an old male it will roost in the same part of the branch on the same tree that it has done for most of its life. Its old girlfriends look forward to renewing acquaintances and making babies. This is the life of bats.

Bats find an amazing number of places to hide during the day. Researchers inspect every nook and cranny in their study area.

‘How do bats do what they do?’ is the question that we authors ask ourselves, again and again, even after 90 years of combined lifetime study. Through this book we want to pass on as much of our accumulated knowledge as possible. However, although we are considered experts, we still wear our L-plates, and will probably die with them. Yes, we are passionate about bats, and we are lucky that they have also been the reason that we have seen most of Australia. They have taken us to places far and wide in this country, so in the first section of this book we want to show you some favourite bat places. Whether you live in a city or in the bush, you will have been closer to these amazing animals than you would realise. We take you along a path that tells you how these incredible mammals function, and how they fit into their – and our – environment. Some readers may be concerned about bats, scared because of stupid myths and legends, but fear not – neither of the authors have caught a disease, we haven’t had bats tangle in our hair, nor have we had one latch onto our throat for a feed of blood. But it’s not just us. In 60 000 years the traditional owners of our land, custodians of our bat fauna for millennia before European settlement, have never had a negative story about bats in their entire history. Welcome to the world of the most unique and interesting group of our nation’s wildlife.

Two Ghost Bats clinging on the wall of an abandoned mine in the Northern Territory.

Researchers radio-tracking flying-foxes in Torres Strait to study migrations from New Guinea.

Significant events in bat research history

Although bats had been collected and studied by many noted naturalists since Australia’s colonisation, the first serious bat research conducted in Australia was by Francis Ratcliffe who was brought from England in 1928 to study the supposed economic problem of flying-foxes raiding fruit orchards. His eminent reports are still used today by bat researchers, 80 years later, and his conclusions that they were not economic pests still stand.

It wasn’t until the 1950s that formal studies began again, when it was discovered that bats could carry a bird band clasped to a wing bone. This allowed individuals to be recognised by their own individual number, and mainly through a number of dedicated cavers and biologists over 60 000 were marked and many were recaptured in the next few decades afterwards. We soon began to learn the patterns of occupation and migration between caves, and we also discovered that many species were sensitive to disturbance in their underground homes. Also, we were amazed that some banded bats were still living well over 30 years later!

Small humid caves and rock shelters are favoured roost sites for Dusky Leaf-nosed Bats.

Grey-headed Flying-foxes were once numerous on the east coast of Australia but are now listed as Vulnerable.

In the early days bats were mainly caught using mist nets, or they were shot for museum specimens. Mist nets are long structures with a very fine mesh, but as they can be seen by many species they were not very effective. Another capture tool, the portable harp trap, was invented in the 1980s and quite a few species that had avoided nets were consequently discovered, and some were new to science. Harp traps come in many designs, but rely on being set in a bat flyway – such as along a track in forest. Most bats cannot detect the fine fishing lines that stop their flight and contain them while they slide into a bag from which they cannot escape.

Greg Richards assembling a harp trap in secondary forest in New Guinea.

Although being a basic tool for many years, by the 1990s bat detectors were sophisticated enough to allow individual species to be identified without having to catch them. The calls that bats use to navigate when flying are usually at frequencies higher than humans can hear, but each species has an individual call, just as birds have. Bat calls can be recorded and analysed with a computer. Using this tool, scientists could for the first time get an idea of what actually happened in the night sky, which opened our eyes to the way that local communities were made up of many different species. Some species that were hard to catch and thought to be rare, were in fact revealed by detectors to be very common, especially the ones that flew high in the sky out of range of nets and traps.

A good night’s catch in a bat trap means a long night’s work for researchers.

The technological world has advanced faster than we can at times believe, and it is amazing to think that the first researcher to study flying-foxes tracked them with a motorbike and a paper map, but now we can sit in an office and track them by satellite systems, or we can follow tiny forest bats with radio transmitters that weigh less than half a gram. In our early days we counted cave bats by eye inside the cave, nowadays thermal imaging cameras and missile tracking software count them with superb accuracy as they fly out at dusk.

An Anabat detector linked to a display module shows bat calls as they happen.

Bat bioregions

Scientists use the concept of bioregions to define areas that have habitats and species groups that are unique to others in any particular landmass. Hundreds of bioregions have been defined Australia-wide, but for the purposes of indicating the main areas for bats in in this country we have distinguished a group that encompasses the nation’s tropical, temperate and arid zones, plus a few salient others. These include:

Cape York and the Wet Tropics, where the primary bat habitats range from open savannah to tropical rainforest. Within the Cape York bioregion is another of world importance, the Wet Tropics World Heritage area, which is unique and incredibly significant for its plants and wildlife.

The Top End and Kakadu, where the primary habitats are savannah woodlands interspersed with spectacular gorges and watercourses, but within this part of the Northern Territory is Kakadu National Park, a site of world significance and containing some unique species of bats.

The Kimberley is an extremely ancient area that was elevated 400 million years ago when the northward-moving Australian tectonic plate collided with the Sunda Arc. The presence of an ancient sea floor, compressed into limestone, is now protected in the Devonian Reef National Park and provides a myriad of roost sites for cave bats.

Our Deserts make up our major bat bioregion, and in our Travelogue (Chapter 2) we also include unique arid areas such as the Pilbara and the Nullarbor Plain. Although one would think that such dry habitat would be very poor in bat species, in fact there are many, and some that are only found in the arid zone.

The Great Dividing Range (GDR) is one of our most diverse bioregions, rich in unique bat species and our east coast is the only part of Australia where all of our eight bat families are represented. Although Cape York and the Wet Tropics are part of the very north of this bioregion, we have kept them separate because they are such special areas. Tasmania is included in the GDR bat bioregion.

The Murray–Darling Basin (MDB) contains several of our major rivers, and lies between the GDR and Deserts bat bioregions. Several bats are found in the MDB and nowhere else in the world, though at times it is lush and rich in resources, but more often it is in drought.

Our Significant Islands aren’t really a bioregion, but of the many islands that surround Australia, two, Lord Howe Island and Christmas Island, are highly relevant because they both have unique species that are now extinct.

In 1928, Francis Ratcliffe used binoculars and a motorbike in the first formal study of flying-foxes, 80 years later scientists track them from satellites.

A perfect place to look for bats.

Bradley Law uses tiny radio transmitters weighing less than a gram to follow very small bats at night, and to also locate their hiding spots during the day.

Karri forest in south-western Australia.

Sandstone outcrops in the Top End of the Northern Territory.

Waterhole in central Australia.

Spinifex desert.

Cool-temperate rainforest in Tasmania.

Wet tropical rainforest in north Queensland.

Chapter 2: Travelogue

Cape York – Wet Tropics

We start our bat-discovery journey in Cape York Peninsula because this is where more bat species are found than anywhere else in this country. About 43 (48 per cent) of our species occur here and for a number of reasons, mainly its closeness to New Guinea and also because of its many different habitats. During the Ice Ages (the last one was 20 000 years ago) sea levels were lower than they are today, and the two countries were linked by land. It was easy for New Guinea bats to enter Australia through Cape York, but some of our species also went the other way to add to the New Guinea fauna. Millions of years ago Australia had a lot of rainforest areas but the onset of dry climates caused most of this habitat to retreat to refuges in the wet tropics of far north Queensland, with smaller pockets at Iron Range and McIlwraith Range, and a tiny patch at Lockerbie Scrub on the tip of Cape York. There are also some dense rainforest bands along some of the big rivers such as the Archer. When they came in from New Guinea some of the rainforest-loving bat species got only as far as the Iron and McIlwraith Ranges, others only to the wet tropics, but some went as far as northern NSW.

Each night in the rainforest there are smaller fruit bats also feeding in a way that helps with seed dispersal and pollination, making sure that there are plenty of seedlings to replace old trees as they die or fall over in cyclones. There are strange-looking Eastern Tube-nosed Bats, which have funny round heads with nostrils on tubes, like snorkels. We first thought that the bat used these to breathe while it was eating mushy fruit, but it was instead found to be for quite a different purpose. These bats have a ‘stereo-nose’, discussed in Chapter 5. Basically they have directional smelling, just as humans and other mammals have directional hearing. Tube-nosed Fruit Bats seem to favour the understorey as a place to find their fruit, which is a part of the rainforest that the big flying-foxes can’t get into. Again, these little fruit bats play a service role for the forest, by dispersing the seeds of understorey plants. While the fruit bat army is feeding and dispersing seeds, smaller bats in this family are pollinating flowers to create the fruit. There are two species of these bats on Cape York that look similar with long snouts and very long tongues, designed to lick the nectar from flowers. Just like honeyeaters and bees, pollen attaches to the bats which they then transfer from flower to flower, and from tree to tree. If you look at the photo of the Bumpy Satinash, you can see that the flowers come out of the trunk, instead of growing on the tips of branches. Trees like this are visited during the day by birds and by blossom bats at night. The Bumpy Satinash and many other trees make most of their nectar at night, especially to attract these bats, which are their main pollinators. Insect-eating bats also abound on Cape York Peninsula, where there are about 38 different species in various shapes and sizes, and in all of the different habitats. Some are specially designed to flutter around in the densely packed rainforest vegetation, and there are others that fly much faster and mainly use the woodlands but also fly above the rainforest canopy. Rivers, creeks and billabongs are preferred places for woodland bats to feed, mainly because of the concentration of insects that hatch from the water or mud. There is also a small bat that loves feeding on insects and probably tadpoles in the water, and it even takes the occasional tiny fish. This bat, the Large-footed Myotis, has special flattened toes and it drags its feet like a rake through the water. On a hot night, camped by a creek with lots of ponds, you can often see groups of these bats skimming over the water, occasionally dipping into the surface.

The Fawn Leaf-nosed Bat that was first discovered in the mid-1800s on Albany Island, off the tip of Cape York, frequently has an orange-colour phase.

A Tube-nosed Fruit Bat homes in on a cauliflorous (trunk-fruiting) fig that it locates with directional smelling.

Another association between bats and man on Cape York Peninsula has been through mining. There are many Cape York species that prefer to live in caves than in tree hollows and when a gold rush came, or a tin deposit was found, new homes for bats were made. One of the big limestone cave areas in this region is around the Mitchell–Palmer Rivers, and this is one of the main areas where the meat-eating (carnivorous) Ghost Bat can be found. This bat, which feeds on birds, smaller bats – in fact anything it can catch – needs a variety of different caves. They need big open ones as a nursery when they breed each summer in large groups, and smaller caves when they move away in winter in small groups. As well as many of the mineshafts around Cape York being used by small groups of Ghost Bats, some mines contain big colonies of horseshoe and leaf-nosed bats. These unusual-looking bats have special fleshy parts around their nostrils that help to direct and beam out their calls, and they generally like very warm and humid caves or mine tunnels, so warm and wet that water drips off the walls. We think that this type of environment stops their fine wing membranes from drying out. One of the conservation problems for these types of bats is that they are very scared about predators when they are confined, so human disturbance is a big issue. Sometimes, regular disturbance by people can force a colony