Facts about flying foxes
The following general information about bats is largely provided by the New South Wales Ku-ring-gai Bat Conservation Society Inc.
Included on this page:
- general information
- microbat information
- megabat information.
A bat is a flying mammal, not a bird. Bats are the only flying mammal.
There are over 1,000 species of bats in the world belonging to the order Chiroptera (which means 'hand winged').
These can be divided into two suborders:
- megabats (Megachiroptera), of which there are about 170 species
- microbats (Microchiroptera) which make up the majority of bat species.
One quarter of all mammal species in the world are bats, and in Australia there are over 90 species.
Bats vary in weight from a few grams for the smallest bats to the largest flying-foxes which weigh over one kilogram.
The smallest bat species have a wingspan of about 20 millimetres while the largest reach almost 2 metres.
Bats hang by their feet with their head down because it is energy efficient.
In order to reduce as much weight as possible for flight, the bones and muscles of the legs are very light weight compared with those of a non-flying mammal of comparable size.
The biggest bones and muscles are those used for flying.
The wings of bats are made of two thin layers of almost hairless, soft, strong, elastic skin which stretches between very elongated finger bones and joins the side of the body from the arm to the ankle.
In microbats the membrane extends between the legs and includes the tail. These wings contain blood vessels and nerves.
They stretch easily for flight yet contract when not in use.
Different bat species have different wing shapes depending on where and how they catch their food.
Bats are mammals but do not have a pouch. Only marsupial mammals have a pouch.
Bats are eutherian (placental) mammals.
This means that their babies are born fully developed and are nourished on their mother's milk, just like humans.
One of the easiest ways to distinguish microbats and megabats is diet.
Megabats are larger and feed on nectar, pollen and fruit. Flying-foxes belong to this group.
Microbats are smaller and are usually insect eating, carnivorous bats.
All bats feed at night. Scientists believe that microbats evolved from small, nocturnal mammals to feed on night flying insects, therefore avoiding competition with birds that are active during the day.
Megabats, which feed on night-flowering, nectar-producing plants, may have evolved from different ancestors.
The oldest fossil bats known in the world are microbat fossils.
Fossil teeth found at Murgon, Queensland, Australia, date back 55 million years.
Other microbat fossils found are:
- Icaronycteris foundin Wyoming, USA, dated to 50 million years
- Archaeonycteris foundin Germany, dated about 45 million years.
Some bat fossils are so well preserved that remains of insects and other small animals that they had eaten can be seen inside the body.
The rich Australian fossil beds at Riversleigh in north-west Queensland contain many microbat fossils up to 25 million years old.
Megabat fossils have been found in Thailand, Italy, Africa and New Guinea, but have not yet been found in Australia.
Bats in Victoria
All Victorian native wildlife is protected under the Wildlife Act 1975.
This includes microbats and megabats.
Nationally threatened species are afforded extra protection under the Commonwealth Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act).
Of the bat species found in Victoria, the southern bent-wing bat is listed as critically endangered nationally and the grey-headed flying-fox and south-eastern long-eared bat are listed as vulnerable under the EPBC Act.
Bat species listed as threatened in Victoria under the Flora and Fauna Guarantee Act 1988 are:
- common bent-wing bat
- south-eastern long-eared bat
- grey-headed flying-fox
- eastern horseshoe bat
- yellow-bellied sheathtail bat.
Microbats (sub-order Microchiroptera)
Bats from this group are found on all continents across the world except Antarctica.
In Australia there are many species of microbats ranging from the carnivorous ghost bat, the largest, which weighs up to 150 grams, to tiny forest bats weighing just three grams.
Microbats are important because they eat vast numbers of insects, thus contributing to the control of insect populations in the natural environment.
This is important because microbats control many insect pests of crops and insects that spread disease such as malaria.
Each species of microbat eats different sized food including mice, frogs, other bats, small birds, fish, large grasshoppers, moths, caterpillars, beetles, bugs, spiders, scorpions, cockroaches, flies, ants, mosquitoes, termites and gnats.
On the American continents there are microbat species which also feed on fruit, flowers and blood.
Microbats are able to find their way in the dark and catch their food using echolocation.
High frequency sound pulses made in the larynx (voicebox) are emitted either through the nose or mouth.
Echoes of these calls reflected back to the bat's ears allow it to know the position, relative distance and character of objects in its environment.
The echolocation sounds are nearly all above the hearing range of people.
Microbats use other calls for communication particularly in the roost.
Some microbat species live in caves in large colonies.
Other species roost in hollows in trees, under bark, in small holes in logs or fence posts, in bird's nests, under bridges, or in the roofs or walls of buildings.
Radio-tracking of individual microbats has shown that they use a number of different roosts in an area.
Microbats rarely move about in daylight, but venture out to hunt for food at night.
Most microbats catch prey in flight but a few species hunt on all fours for ground living invertebrates.
In winter there are few insects about so microbats in cold climates such as southern Australia save energy by hibernating.
When hibernating, microbats roost in a cold, sheltered place, and are able to drop their body temperature close to that of their surroundings and slow their heart rate.
Disturbance of hibernating bats can cause them to return to operating temperature.
This uses up fat reserves, which they need to survive until there are enough insects to feed on.
Disturbance of hibernating bats can cause death.
Microbats can also use torpor which is similar to hibernation, but used only for a few hours or days to conserve energy when food is scarce.
Microbat babies are born in the spring and summer when days are warm and food is plentiful.
Most species give birth to one young per year.
Newborn microbats are not furred and their eyes are closed at first. By six to eight weeks, they are fully developed and able to fly and feed with adults.
Some species give birth in maternity caves where the shape of the cave roof traps the body heat of the adults so that the unfurred young are able to survive when the mothers leave them to feed at night.
Some maternity caves are known to contain hundreds of thousands of bats.
Other species form maternity colonies in the hollows of big old trees or in buildings. Mother microbats, which roost in tree hollows, carry their babies from one hollow to another.
This behaviour may be to avoid predators or it might be to avoid a build up of parasites, or both.
Megabats (sub-order Megachiroptera)
Megabats are large bats that navigate by sight and smell and feed on plant products. They can be found in Africa, the Middle East, Southern Asia, Australia and many islands.
In Australia there are 12 megabat species including:
- tube-nosed fruit bats
- blossom bats.
Of the eight species of flying-fox there are four widespread species occurring on the mainland of Australia. These are:
- the black flying-fox
- the spectacled flying-fox
- the grey-headed flying-fox
- the little red flying-fox.
The first three species have similar habits and lifestyle but are found in different parts of Australia, their ranges overlapping in part.
In contrast, the little red flying-fox is smaller, gives birth at a different time, and tends to follow the flowering of the eucalypts inland, moving to the coast irregularly.
Flying-foxes as primates
The theory that flying-foxes are related to lemurs, lorises, monkeys, apes and man (primates) was proposed by Dr Pettigrew at University of Queensland.
This theory is based on studies of the brain and nerves to the eye that show the structure a flying-fox brain is more like that of a primate than a microbat.
Dr Pettigrew proposed that the megabats and microbats evolved from different ancestors and that the structure of the wings of these two groups of bats has evolved independently (known as convergent evolution).
The majority of flying-foxes feed during the night within a radius of 30 kilometres from their camp, however, when feeding on blossom they may travel up to 100 kilometres.
Some flying-foxes feed in the same place on successive nights.
The main source of food for flying-foxes is nectar and pollen from the flowers of native trees, such as the many species of eucalyptus, as well as turpentines, paperbarks, and banksias.
Pollen is the major source of protein for flying-foxes. Flying-foxes often lick pollen from their fur while grooming.
Flying-foxes also eat fruit from many rainforest plants, such as figs and lilly pilly.
They chew the fruit to extract the juice. Flying-foxes swallow fruit juice and some small seeds up to four millimetres in diameter.
Nectar and fruit juice provide flying-foxes with carbohydrates and sugars required for energy.
At times, flying-foxes chew leaves of plants such as mangroves and figs and can feed on non-native fruit and flowers.
Flying-foxes have a very short intestine and absorb their mostly liquid diet very rapidly.
The average time from mouth to anus is about 20 minutes although some material takes up to an hour.
This is important for seed dispersal because the small seeds contained in the faeces (poo) fall and germinate in new areas leading to new trees and vines.
To drink, flying-foxes swoop down to belly-dip in rivers and dams. They then land on trees and lick the water from their belly fur. They also lick dew from leaves.
Importance for the ecosystem
Flying-foxes are essential in maintaining ecosystems because they can move pollen and seeds over long distances and across cleared ground, linking patches of native vegetation.
The clearing of native vegetation in the last two centuries has removed much vegetation and has left the remainder scattered in isolated patches.
Birds and insects often don't fly the long distances required to transfer pollen or seeds between vegetation patches.
Flying-foxes carry pollen on their fur between flowering trees that can be many kilometres apart.
Many Australian trees, especially eucalypts, need pollen from another tree of the same species to make fertile seed.
Rainforest seeds are carried away from parent trees which gives them a chance to germinate and grow.
Speed and distance of flight
Flying-foxes also use the wind to travel long distances and have been recorded at speeds of 50 kilometres per hour.
Radio-tracking of grey-headed flying-foxes found that in 1990, one moved from Grafton to feed on the flowers of spotted gum near Narooma, about 800 kilometres south.
Another flew from Lismore to Bundaberg in Queensland, about 400 kilometres to feed on lemon-scented gum.
By tracking a few individual flying-foxes by satellite it has been found that individuals travel great distances.
For example, one flying-fox moved from Melbourne to Mallacoota then north along the coast, stopping at Ulladulla and Jamberoo, then to Sydney, where it moved between several more camps.
In camps, flying-fox numbers increase and decrease throughout the year, depending on the availability of food.
The flowering of many species occurs irregularly in different areas and different times of the year, governed mainly by variations in weather.
Tracking information is recorded in:
Augee M and Ford D (1999) Radio-tracking Studies of Grey-headed Flying-foxes, Pteropus poliocephalus, from the Gordon Colony, Sydney.
Flying-foxes see very well during the day and much better than humans at night.
With relatively large eyes in the front of their skull, their acute eye-sight enables them to navigate accurately and to find food at night.
Many of their food plants have white blossom making them easy to see when flying above the trees at night.
In daylight flying-foxes are also able to fly and land on branches within the camp and use sight during social interactions in bright sunlight.
Flying-foxes use their excellent sense of smell to locate nectar and ripe fruit.
They also recognise each other by sight and smell.
Flying-foxes have scent glands on their shoulders, and the scent is spread over their body while grooming.
Males rub their scent glands onto tree branches in the colony to mark a territory, and mothers recognise their young by their calls and by their smell.
Flying-foxes also sniff each other during social interactions.
While sight and smell are very important to flying-foxes, evidence suggests hearing is of less importance.
Unlike the complex ears of microbats, flying-foxes have a simple external ear.
The part of the brain which controls hearing is small in flying-foxes compared to that in microbats.
The area occupied by a population of flying-foxes is called a camp or a colony.
A camp may contain a few hundred to tens of thousands of flying-foxes.
Flying-foxes move to alternative camps when food is not available nearby. Most of these camps have been in use for more than 100 years.
During the day, they roost together in the tops of trees.
During the roost, they spend some time sleeping, often hanging by one foot, with their wings wrapped around their body.
Flying-foxes also spend many hours each day grooming, squabbling noisily and fanning themselves.
Predators known to eat flying-foxes include:
- carpet pythons
- powerful owls.
Currawongs and ravens are known to attack flying-foxes found alone in the daytime.
These predators do not significantly reduce the overall flying-fox population.
The most likely victims are the young, the sick or old.
The numbers taken are small relative to the flying-fox population.
Predators contribute to the health of a population by removing the least fit individuals.
Humans and their technology are responsible for more flying-fox deaths than natural predators.
Many flying-foxes die as a result of the removal of habitat, shooting, or electrocution (on power lines).
Flying-foxes are social animals and make a wide range of calls.
These include contact calls, chirps and squabbles, searching calls (by mother flying-foxes seeking their young), and a range of mating and warning calls.
At night feeding flying-foxes are often heard in flowering or fruiting trees as they compete for food.
Australian flying-foxes do not echo-locate; that is, they do not use sound to locate or navigate.
Little is known about what age the majority of flying-foxes reach in the wild.
Records of banded flying-foxes indicate that some live for up to 12 years in the wild.
The oldest captive educational grey-headed flying-fox, cared for by Ku-ring-gai Bat Conservation Society, was born in 1978 and died of old age in 2000, aged 22.
Several other captive flying-foxes have lived to similar ages in captivity.
Natural disasters, such as the high temperatures and low humidity that occurred in Sydney in January 2002, have killed thousands of flying-foxes of all ages.
Flying-foxes groom their fur frequently with their claws and lick their wings.
They urinate on themselves to wash and in the summer they urinate on themselves then fan their wings to cool down.
Like all mammals bats are hosts to tiny parasites that live much of their life cycle on the animal.
Bat flies are wingless flies, only a few millimetres long, which are adapted to avoid being groomed out of the fur by the bat or blown off during flight.
They feed on the bat's blood. They are species specific and cannot live on other mammals such as humans.
Flying-foxes also have internal parasites which have adapted to live in the flying-fox population without causing undue illness in their hosts, except during times of food shortage.
One is a worm (Toxocara pteropodis), which is transferred with the milk from mother to young and from young to adult through faeces on branches. Again this organism cannot live in humans.
Occasionally flying-foxes are hosts to ticks and mites. In Queensland a number of spectacled flying-foxes die each year from tick poisoning.
Mating occurs between March and May.
Males mark a territory in a tree and defend it from other males during the summer and autumn.
They are joined by females, many with young. Males guard several females in their harem.
Harems are generally unstable groupings, with the females moving, at will, to other males.
After becoming pregnant in autumn, flying-foxes give birth in the spring (mainly October – November).
Flying-foxes give birth in the tree tops, usually in the colony and one baby is born to each female.
The baby is born furred and with its eyes open. It weighs about 80 grams at birth although birth weight varies according to the availability of food for the mother during her pregnancy.
The female has two nipples, one on either side of her chest beneath the wingpit.
As soon as the baby is born it begins to suckle. Its milk teeth curve backwards so that it can keep a firm hold.
The female protects her baby with her wings during the daytime.
At night when she flies to search for food the baby holds onto its mother, with its mouth around the nipple and with its claws in her fur.
The baby is not able to maintain its own body temperature until it is 15 to 17 days old so for about a month is carried by the mother while she feeds at night.
The young are then left in the camp during the night.
Young flying-foxes gradually increase their flying skills. By 12 weeks they are able to explore the local area around the camp, then increase the distance until they are flying out with the adults to feed.