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By Thea Williams 30 May 2019 9 min read

David Westcott has been working with flying-foxes for 20 years. Image: CSIRO / Nathan Dyer ©

THERE are certain animals most of us love to hate. And then there are people who dedicate their careers to them.

David Westcott has spent the best part of 20 years researching flying-foxes.

Flying-foxes feed on fruit, flowers, pollen and nectar, and play an important ecological role in seed dispersal and pollination.

They also have a reputation for congregating in camps, or roosts – often in very large numbers.

Regional papers, in Queensland and New South Wales in particular, frequently voice the concerns of residents who suddenly find their space invaded, and of orchardists and farmers whose crops provide fruitful hunting grounds.

In February this year, the spectacled flying-fox was moved up from vulnerable to endangered, joining the critically-endangered Christmas Island flying-fox on Australia’s national endangered list under the Environment Protection and Biodiversity Conservation Act.

Westcott says that during his years of work studying flying-foxes, he’s learned plenty about humans, nature and conflict. He says the endangered listing of the spectacled flying-fox is a disappointing necessity and a prompt for us to think about how we, as communities, interact with the world around us.

Community conflict

Anecdotal records of problems posed by flying-fox colonies go back to the early days of settlement, says Westcott.

An article in the Sydney Gazette during the drought of 1811 feared a repetition of the “so dreadful a calamity” of 1789 when thousands of flying-foxes died in a heat stress event and fouled the water supply of the new settlement.

Articles since then have bemoaned the impact on crops and in towns, such as this comment penned from Duporth, Queensland, in 1896:

“With the ripening of the fruit crops, the much-discussed question—the destruction of flying-foxes, or protection of fruit from their depredations— is sure to arise.” Thomas O’Connor, Letters to the editor, The Queenslander.

In 2019, the conversation continues.

In Coombabah on Queensland’s Gold Coast, residents “are being driven batty by a roost of flying foxes at Chiba Park” and in Orange, NSW, there’s the “annual infestation of grey-headed flying foxes in our parks, orchards and vineyards”.

Says a letter to the editor: “I am not advocating the wholesale slaughter of these animals. I'm simply asking for action to move them out of our inhabited cities and back into the bush where they belong. There is still plenty of forest out there for them to live in.”

Call for monitoring

A century after that letter to the editor in The Queenslander, David Westcott started working for CSIRO in Atherton and spectacled flying-foxes were again an issue in Far North Queensland. The issue of accurate population counts for the spectacled flying-fox was central to the public debate.

“It was a difficult debate, not going anywhere, and seemed hung up on whether the flying-foxes were declining or increasing,” he says.

“No one trusted each other’s claims about what the population was doing, so to progress we needed monitoring methods.”

But it’s hard enough conducting a census of humans, let alone flying foxes.

Flying-fox colonies are not one big happy family but a collection of individual animals that come and go. Image: CSIRO / Nathan Dyer

They’re difficult to detect beyond known roosts, extremely mobile and seem to respond suddenly to changes in available food sources.

Westcott and colleague Adam McKeown developed a monitoring method for estimating abundance and trends of flying-fox populations, based on ground counts using trained counters. This led to regular monitoring of the spectacled flying-fox since 2004. In 2012, with the addition of the grey-headed flying-fox and east coast black and little-red flying-foxes, this program became the National Flying-Fox Monitoring Program with participating state and territory environment departments collecting data from councils, community groups and individuals, and forwarding it to CSIRO for analysis.

Analyses performed by Peter Caley at CSIRO shows that the grey-headed flying-fox populations appear to be fairly stable. However, since the spectacled flying-fox survey began in 2004 there has been a large decrease in its population, hence their listing as endangered. Population modelling suggests that the decrease in the spectacled flying-fox population was driven by the long-term effects of severe cyclones. Last summer’s extreme heat events resulted in the deaths of an estimated 20,000 animals, a large proportion of the remaining population. Heat stress mass mortality events have been increasingly affecting other flying-fox populations, however this event was the first time it has been recorded in spectacled flying-fox.

More than numbers, where do they travel?

Monitoring isn’t just about numbers, it is also about understanding how the animals are distributed across the landscape, and part of that is learning about their movements.

CSIRO’s Adam McKeown started working with Westcott in 2001 and says early attempts at radio tracking provided some insights into the distances flying-foxes travel. However, radio tracking requires the researcher to physically follow the “signal” to where the animal is feeding, so for animals as wide ranging as flying-foxes it requires huge amounts of field time and night-time mileage to collect the data.

Technological improvements mean that these days they use satellite telemetry, with the animals’ overnight movements arriving in an email each morning – it’s not as romantic, but much more productive, says McKeown.   This data is cross-referenced with detailed information on vegetation, to see what is driving the movement of the animals.

“They’re a fascinating animal, with these really interesting and massive movements,” says McKeown.

Eric Vanderduys and Adam McKeown taking a blood sample from spectacled flying-fox for disease analysis. McKeown says his favourite are the little red flying-foxes. "They’re feisty so you’ve got to be alert, occur in huge numbers, and there’s so little known about them."  Image: CSIRO / Nathan Dyer ©

Recently, Westcott and his team were funded by the Queensland Government to monitor little red flying-foxes around Charters Towers.

So far, they’ve fitted 37 satellite trackers to little red flying-foxes and results show the animals are travelling thousands of kilometres in the pursuit of flowering food trees — some have been tracked to the Cape York Peninsula and onto the Northern Territory, while others flew south to Brisbane, and even to the Hunter Valley in New South Wales.

Capturing flying-foxes for tracking also allows for collecting tissue/blood, pollen and other samples for use in analysing their life histories and food trees used.

Perpetual backpackers

Critical in understanding the behavior of flying-foxes is the fact that they don’t live the way we expect, says Westcott. The flying-foxes which appear to arrive in large groups to roost are not, in fact, one big happy family.

Westcott calls them “perpetual backpackers” that usually spend a week to 10 days in any one camp before flying on.

“Those camps aren’t homes, they’re more like motels,” he says.

“Animals will fly in and then fly on, following the food resources. That has fundamental implications for how we go about monitoring them – and critically for how we manage them. Scaring them away from a roost doesn’t often work because new animals are constantly turning up, and those new animals don’t know that they aren’t going to be welcome. Since it is likely that most animals in the population are familiar with many, or even most, of the camps used by the population there are a lot of potential newcomers that could turn up after an attempt to scare them away.

“And why would they turn up? All the evidence indicates that they are following resources. They turn up in big numbers where there are abundant nectar resources and flowering events seem to attract them from thousands of kilometres away. We know that they have very good spatial memory and they may even remember that certain areas are good at certain times of the year and then, once they are in an area, their excellent sense of smell helps them navigate to their next meal.

“Ultimately, we would like to be able to predict their arrival so that communities can prepare before they arrive.”

Measuring forearm length of a spectacled flying-fox to determine age class. Image: CSIRO / Nathan Dyer ©

As McKeown explains, it appears that all four mainland Australian flying-fox species are increasingly attracted to urban areas, though the reasons are unclear.

The animals generally feed kilometres away from where they camp, therefore there are two questions at different scales.

“What drives the animals to be in the region? This seems to be food resources. And then when in the region, why do they choose to camp in someone’s backyard, often tens of kilometres from where are feeding.”

The team has been studying camps right across the state looking at what sort of roosts species choose.

“If we wanted to build an alternative camp, what attracts them? And how can we make problem camps less attractive without losing the urban trees we love?” says Westcott.

Working with flying-foxes – and communities

While Westcott is fascinated by flying-foxes he also acknowledges that they worry many people in the community and that concern about diseases carried by the flying-foxes is a big part of this.

“All animals carry diseases, including our pets, domestic animals, and us. Flying-foxes are no different. It is worth remembering though that non-indigenous Australians lived with flying-foxes for nearly 200 years before realizing that the animals carried significant diseases. This means that the risk of contracting these diseases isn’t great, even if the consequences of contracting them is.

“In our everyday life we face many similar situations, like crossing the road or driving the car, activities where there is a risk with high consequences. In those situations, rather than living in fear we adopt very simple precautions that minimize the risk, like road rules and looking both ways. With flying-foxes those rules are; don’t handle bats, wash the wound and seek medical advice if you are bitten or scratched, keep your horses vaccinated and out from under bat roosts or foraging trees.”

The 1896 letter to the editor in The Queenslander said: "Parties of shooters also have been organised, who have raided camps of foxes, and successfully destroyed large numbers of them, although at the cost of considerable time and expense. This method, as yet, has been considered to be the best means for grappling with the evil, but it is questionable whether this plan is a feasible one." Image: CSIRO / Nathan Dyer

And working with people?

"Understandably, people who live under flying-fox camps get fed up with them and communities often demand immediate and dramatic action. Moving a camp can work sometimes but we have over 100 years of experience to show that more often it is an expensive waste of effort.

“A lot of what we do nowadays is to try to get councils and communities to think hard about the nature of the problem they are facing. You don’t need to love or even like the animals to understand what their ecology and behavior means for how you go about dealing with them.

“A key issue for us, and for communities, is to figure out when moving a camp is a reasonable choice, and, when it isn’t, how to make living with it as easy as possible.”

Spectacled flying-fox

The Spectacled Flying-Fox (Pteropus conspicillatus) was first scientifically described in 1850 by John Gould and, when listed earlier this year, joined another 37 mammals added to the Australian national endangered list.

The spectacled flying-fox has required a lot of detailed modelling. The National Flying-Fox Monitoring Program is a collaboration between researchers, governments and volunteers from Adelaide and anti-clockwise around the coast to Broome.

“For me it’s disappointing that it’s been listed, it’s a signal failure. It means the species is in trouble, that’s not a good thing,” says Westcott.

“I think this is a species that needs help and we should be thinking about how we do that. This listing makes it easier to turn that into action.”

Read more on the National Flying-Fox Monitoring Program

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