We hear a lot about flying foxes in Australia, but for all the wrong reasons.

Bats usually only hit the headlines when a loud colony moves into a quiet neighbourhood.

But behind the screeching and the [exaggerated] threat of disease, these mega-bats are a phenomenon of evolution and are absolutely essential to maintaining healthy ecosystems in Australia.

The only true flying mammal

Flying fox wings are actually skin stretched between fingers. ( Supplied: Jurgen Freund )

Although some mammals and marsupials like flying-squirrels and Australian gliders can leap from heights and glide, bats are the only mammal that can sustain genuinely powered flight.

Known as mega-bats, as opposed to the micro-bat family that includes such species as the bare-rumped sheathtail bat and the tube-nosed insectivorous bat, flying fox wings have evolved from their hands, with a thin membrane of skin stretched between each finger. The order Chiroptera of which bats are a part, literally means "hand wing".

They first appeared in the fossil record about 50 million years ago, and analysing the skeleton clearly shows the evolution of the hands according Western Sydney University senior lecturer Dr Justin Welbergen.

"When you look at their skeletons, you can clearly see they have four fingers and a thumb with a membrane grown between it," he said.

Life in the upside down

Bats have locking mechanisms in their legs that allow them to hang upside down without using energy. ( Audience submitted: Barb Leopold )

Although we just kind of accept that bats do it, spending half your life hanging upside down is pretty weird.

But as Dr Welbergen explains, it also makes a lot of sense.

"Bats have a special tendon with a ratchet-like locking mechanism in their legs which allows them to hang securely without expending any energy," he said.

Unlike birds which can easily take off from a standing position, bats typically drop from heights before taking flight, so hanging upside down means taking off is just a matter of letting go.

"Hanging upside down … has enabled the wings, over evolutionary time, to become completely dedicated to powered flight," Dr Welbergen said.

When you spend half your life upside down, you have to be able to get on with just about any task while inverted. And that includes sex.

To mate upside down, females hang onto the males by the ankles, while he grabs onto her neck with his teeth.

Males compete fiercely during the breeding season, marking out territory with scent glands in their shoulders.

But despite all the effort, copulation is pretty short lived and when it's over, the female will take off in search of another mate.

Is that a nipple under your arm or are you just happy to see me?

Maternal behaviour is very strong in flying foxes. ( Getty Images: Manuela Schewe-Behnisch )

Flying fox mothers typically give birth to a maximum of one baby every year.

Although there are instances of twins being born, the chance of both offspring surviving is extremely low.

Because newborns are entirely dependent on their mothers in the first few months of life, they cling to her when she goes off foraging at night.

To get a solid grip, they hang onto her nipple located under her wing, and grip around her waist with their hind legs.

Perhaps because of their low reproduction rate, the maternal instinct of flying foxes is incredibly strong.

After losing their babies to predators, mothers have been observed flying and calling in the area where they last saw their young for up to a week.

Trees entirely dependent on flying foxes for reproduction

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"There are quite a few species of eucalypt that only produce nectar at night," Dr Welbergen said.

"These species are by and large dependent on flying foxes."

A study of eucalyptus species within Kakadu National Park found pollination by the black flying fox and little red flying fox was integral to "the maintenance of genetic diversity" and "the long-term survival of native forests".

Unlike other pollinators like bees and flies, flying foxes are able to transport pollen vast distances, and are also able to disperse larger seeds.

They have a very rapid digestive system, and are known to pass seeds within half an hour of eating.

With two of Australia's four species — the grey-headed and spectacled flying fox — listed as vulnerable under Australia's Environmental Protection and Biodiversity Conservation (EPBC) act, Dr Welbergen said their extinction could be catastrophic.

"That would reverberate throughout Australia's forest ecosystems. It would have profound implications."

He says habitat fragmentation due to land clearing is already having a significant detrimental effect on their wellbeing.

Check out the flying foxes streaming right now on ABC Wild Oz.