Melbourne’s flying night gardeners

 

As the sun finally dips below the horizon, the small crowd that had gathered on the hill to see Melbourne’s skyline silhouetted by a glorious summer sunset slowly starts to drift away. If only they had waited another 15 minutes they would have witnessed something much more spectacular, something much more memorable, and something much more unique than just another sunset over a big city – the daily exodus of up to 50,000 Grey-headed Flying-foxes making their way from their urban sanctuary to the suburbs of Melbourne and beyond.

The Park Ranger responsible for their Melbourne home at Yarra Bend Park, zoologist Stephen Brend says “I don’t think most people appreciate how lucky we are to have this right on our doorstep, just 5km from the city. What an incredible spectacle it is to witness flying mammals, with wingspans of over a metre, crossing a major city at night. I’ve worked all over the world, and seen the animal migrations in Africa, but this fly-out is certainly one of my favourites wildlife experiences, and so easily accessible to everyone to watch”.

But why do they fly out and where are they going? Well, like many Melbournians, they are heading out for dinner, but in this case hoping to feed on the pollen and nectar of our flowering eucalypts and native hardwoods (such as banksias and melaleucas), as well as native rainforest fruits. Of course you can’t always get the meal you’re looking for. Sadly these trees and plants are not as plentiful as they used to be, and so the flying-foxes will also turn to eating the more ‘exotic’ introduced fruits commonly found in our gardens. But whether eating native or exotic food, it’s when they drop in for dinner that most people get their first close-up encounter with these amazing flying mammals. Also commonly known as a fruit bat, the Grey-headed Flying-fox (Pteropus poliocephalus) is a ‘megabat’ and one of four mainland species of flying-foxes found in Australia, along with the Black Flying-fox (Pteropus alecto), the Spectacled Flying-fox (Pteropus conspicillatus), and the Little Red Flying-fox (Pteropus scapulatus).  

Flying-foxes differ markedly to the smaller bat species. As Dr Justin Welbergen, President of the Australasian Bat Society explains “Most smaller bats tend to roost in dark places like caves, mines, tree hollows and under bark, and rely on echolocation to navigate and find food (usually insects). Many don’t travel long distances in search of food but rather hibernate when supplies are low. Flying-foxes, however, roost in amongst the branches of tall trees, possess keen eyesight and a powerful sense of smell, and travel epic distances in search of ephemeral sources of nectar, pollen and fruit.”Highly social and intelligent mammals, Grey-headed Flying-foxes can live for up to 20 years in the wild and typically give birth to just one pup per year, normally between September and December.

Being highly social means they also tend to roost in large groups. These gatherings are not only important for social interactions, but are also a place for them to rest and a provide refuge during the significant phases of their annual lifecycle, such as mating, giving birth and raising their young. Although generally used intermittently, some flying-fox camps have now been established for more than 100 years – longer than some Australian cities.

THE GREAT NIGHT GARDENER
Whilst an incredible spectacle to watch, this daily nocturnal excursion also plays a vital role in the health of our native forests.

Travelling on average around 20km a night to feed before returning home means that they help disperse pollen and seeds, and in doing so contribute to the reproductive and evolutionary processes of forest communities. In fact, they are our most effective long-distance native pollinators and seed dispersers, at least as important as the other well-known pollinators such as birds and bees, who are often given all the credit for this role. Indeed Grey-headed Flying-foxes have been recorded travelling between and Melbourne and Sydney in just two days – that’s 880kms.

Dr Anja Divljanfrom the Australian Museum says “Grey-headed Flying-foxes are vital for the health of Australian ecosystems. As they feed, thousands of pollen grains collect on their fur and many small seeds collect in their gut. Coupled with their ability to fly long distances each night, this means they provide a great mechanism for cross-pollinating plants and dispersing seeds over large areas– they really are the great night gardeners of our ecosystem”.

This spread of pollen and seeds isn’t only limited to around 20 kilometers a night from an established camp. The trees that flying-foxes rely on for food tend to flower at different times in different parts of the Australian landscape, so local nectar and pollen supplies are generally not stable enough for many bats to base themselves in a single place for the entire year.

As such, as winter approaches in Victoria, many Grey-headed Flying-foxes will leave the safety of their Melbourne camp and move up the east coast in search of large flowering events to help them get through the lean colder months.During this time the Melbourne Grey-headed Flying-fox population that can swell to nearly 50,000 over summer, will drop to between just 2,000 and 5,000. As Dr Welbergen adds “Camps are more like backpacker hostels than stable households, housing a constantly changing clientele that comes to visit local attractions. Camps are connected into large networks through which flying-foxes move in response to changes in local food resources.”

UNDER THREAT
Leaving the safety of their homes in an urban environment in search for food can be extremely dangerous. Natural predators include large birds of prey (e.g. Powerful Owl), large snakes and goannas, but becoming entangled in fruit tree netting and barbed wire, as well as being electrocuted on power lines can take a terrible toll. No one appreciates the impact that these types of human obstacles can have more than Bev Brown. Recently awarded an Order of Australia Medal for her decades of work rescuing and caring for urban Grey-headed Flying-foxes, Bev says “I don’t think people realise how devastating power lines, or inappropriate fruit tree netting, or barbed wire can be to these little mammals. I have rescued over 300 Grey-headed Flying-foxes in the last 10 years, and I’ll never get used to seeing a Grey-headed Flying-fox tear its wings as it desperately tries to untangle itself from someone’s backyard fruit tree netting, or as they hopelessly try and chew their way through barbed wire. I’ve even seen an entangled mum try to chew its wing off in a desperate attempt to escape and get back to its pup in the camp. It’s just heart breaking, and what’s really frustrating, is that much of this trauma is preventable. If people just did a few simple things like use appropriate fruit tree netting or paint the top line of any barbed wire in a bright colour so they can see it, it would make a huge difference.”(see break out box)

Barbed wire, fruit tree netting and power lines are not the only threats to Grey-headed Flying-foxes. Habitat destruction, shooting in orchards, heat stress and camps disturbance has all taken their toll on the Grey-headed Flying-fox population. Seeing the spectacle of 50,000 fruit bats fly overhead may lead many people to think this species is doing just fine, but unfortunately that’s not the case. With a total population now estimated to be somewhere between 320,000 to 435,000 along the east coast of Australia, some believe this number now represents just small fraction of what it once was. Sadly, as a result of this population decline and continued threats, they are now listed as vulnerable to extinction. And of course this decline not only impacts them directly, but also our forests. As Dr Divljan warns“The way we are heading, we may lose this species in the next 100 years. If our aim is to preserve our native forests and unique Australian ecosystems for generations to come, we also have to reverse the decline of these magnificent night gardeners.”

THERE IS HOPE
But there is hope and we can help. Lawrence Pope, author of Some Touch of Pity and President of the Friends of Bats and Bushcare, says “There is a lot we can do and should do to help the Grey-headed Flying-fox, but if we also take care of the forests, we will also help take care of the bats, and of course if we help take care of the bats, they will then help us take care of the forests.”

So the next time a flying friend visits your garden at night, rather than be bothered by the night time chatter, or the nibbling on some of your fruit, consider welcoming them in for dinner. Maybe even consider planting a few more native trees so they’ll come back in the future. It’s always nice to have guests pop over. And of course if you happen to be watching a glorious sunset over Melbourne’s city skyline from somewhere near Yarra Bend Park, maybe just wait a few minutes longer after the sun has finally set. If you do that, then you’ll most likely get to witness something much more spectacular and much more unique – up to 50,000 flying mammals heading out for dinner and, in turn, providing a vital service to our native forests and ecosystems. 

 

SOME FACTS
Conservation status:
The Grey-headed Flying-fox is considered to be a single, mobile population with individuals distributed across Queensland, New South Wales, Victoria, South Australia, Tasmania and the ACT. Accepted population estimates sit somewhere between 320,000 to 435,000, representing a 90%+ reduction since British colonisation. With continued population decline (and with low population growth rates even if optimal conditions existed), this species is listed as:
i) ‘Vulnerable’ under the IUCN red list,
ii) ‘Vulnerable’ under the Australian Commonwealth Environment Protection and Biodiversity Conservation Act (1999) and
iii) Threatened’ under the Victorian Flora and Fauna Guarantee Act 1988

Key threats:
Key threats include:
– Destruction and degradation of foraging and roosting habitats over large areas
– Conflict with people, including deliberate camp disturbance
– Heat stress events
– Entanglement in back yard fruit-tree netting
– Entanglement in barbed wire
– Electrocution in power lines

Most don’t know:
Most people are generally unaware that:
– GHFFs are vegetarian
– GHFFs are highly intelligent, social, and caring mammals that breast feed their young
– GHFFs are a vital ‘keystone’ species – meaning that many other species (both plants and animals) rely upon them for their survival and well being
– GHFFs are vulnerable/threatened to significant population decline
– GHFFs are regularly maimed and killed by the largely preventable impacts of inappropriate back yard fruit tree netting and barbed wire
– A significant amount of work goes into rescuing and caring for GHFFs caught in nets/barbed wire
– In Melbourne, during summer at dusk, they create one of nature’s great spectacles – 50,000 flying mammals heading out over a major city at night, looking for dinner!

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