Give me room (Image: Stanley Breeden/National Geographic/Getty Images)

Species: Petauroides volans

Habitat: eucalyptus forests of eastern Australia, passing silently overhead

If you’re wandering around in an Australian forest and see a giant marsupial flying toward you, you’d be forgiven for thinking that someone had spiked your grog. In fact you may be witnessing the flight – technically the glide – of the country’s largest gliding mammal, an unusual marsupial called the greater glider.


To find one, go out into the forests of south-east Australia at the dead of night and shine a powerful torch into the trees. You may see the eyes of a greater glider, glowing in the torch’s beam – the trick is to be able to recognise it purely by the spacing and colour of the eyes, which is all you are likely to see.

There are plenty of gliding mammals in the world, but the greater glider is one of the largest – albeit not quite as big as the south Asian woolly flying squirrel. It is not closely related to any of these other gliders, however: it is the sole airborne member of the ringtailed possum family.

Populous and widespread, the greater glider is nevertheless in great danger. A team of researchers who have tracked the species since 1996 have found that its numbers are in steep decline. They say the greater glider is an example of a oft-encountered problem: species that are common but nevertheless vulnerable.

Tree to tree

Greater gliders grow to 45 centimetres long, or twice that if you count their tails. They look bigger than they actually are, thanks to their thick fur.

They glide using membranes called patagia that extend from the elbows of their front limbs to the ankles of the hind limbs. When they jump from trees they splay their long limbs out wide, and the patagia form a rough triangle that allows them to glide over 100 metres, steering with their tails. The patagia have another use: they insulate the glider, ensuring it does not get too cold in the chill nights of its ranges.

Like koalas, the gliders feed almost exclusively on eucalypts, three groups of trees that include the well-known eucalyptus species. The leaves of these trees are nutritionally poor and laced with toxins, so not many species bother with them.

Because of its poor diet the glider has to eat a lot to get enough calories, but this poses a problem. Gliding animals cannot get too heavy, but digesting a leafy diet demands a big, complex digestive system that can ferment the food and otherwise squeeze every last drop of energy from it. The glider is about as small as it is possible to be while still living wholly off leaves.

On the way out?

Greater gliders occupy thousands of square kilometres, but that doesn’t mean they are safe. Far from it, say David Lindenmayer and colleagues at the Australian National University in Canberra, who have made long-term studies of three greater glider habitats. In the Victorian Central Highlands, the population has been declining by 8.8 per cent every year since 1997, and it appears to have disappeared completely from Booderee National Park in New South Wales since 2007.

The third site, Tumut, also in New South Wales, offers hints of why. There are plenty of patches of eucalypt forest, but they are often surrounded by plantations of Monterey pine. No greater gliders were found in those patches.

The problem for greater gliders is that not only do they need eucalypt trees, they need vast swathes of them. They live on their own, and each animal needs between 1 and 4 hectares. They are also very clumsy on the ground, so struggle to cross cleared ground.

The gliders also need lots of large trees with cavities, which they use as shelters and nests. Tall trees are best, as they are ideal for gliding. Many of these old-growth trees have been logged, however, leaving the gliders without homes.

In fact, the greater glider is Australia’s answer to the giant panda. It relies on a specialised, nutritionally poor diet, and it also needs lots of old-growth forest in which to breed. Fortunately it doesn’t seem to be quite so disinclined to have sex, so there may be hope for it yet.

Journal reference: Biological Conservation, DOI: 10.1016/j.biocon.2011.02.022

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