The Times Australia
The Times World News

.

Grey-headed flying-fox population is stable – 10 years of monitoring reveals this threatened species is doing well

  • Written by Eric Vanderduys, Research Projects Officer, CSIRO
Grey-headed flying-fox population is stable – 10 years of monitoring reveals this threatened species is doing well

Flying foxes, or fruit bats, are familiar to many Australians. So it may come as a surprise to learn two of the four mainland species, both grey-headed and spectacled flying foxes, are threatened with extinction.

But our decade-long survey[1] of one of these species – the grey-headed flying fox – brings some encouraging news. Our data show the population has been relatively stable since 2012, when surveys first began under the National Flying-fox Monitoring Program[2].

Incredibly, the species emerged from the Black Summer of 2019–20[3] relatively unscathed. Flying foxes also suffer in heatwaves and many die, but overall numbers have remained stable.

While this study is good news for the species, we must not become complacent. Heatwaves are expected to become more frequent and intense as the climate changes. Only further monitoring can determine its effects.

Read more: Flying foxes pollinate forests and spread seeds. Here's how we can make peace with our noisy neighbours[4]

Hanging out with flying foxes

The grey-headed flying fox[5] (Pteropus poliocephalus) is common in most cities and towns across south-eastern Australia. More recently, colonies have become established in South Australia[6].

The species can be found anywhere from Maryborough, on Queensland’s Fraser Coast, to Adelaide, with some outlying populations as far north as Ingham in north Queensland. There’s also a breakaway group in Port Augusta, 300km north of Adelaide.

Map of grey-headed flying fox counts. Minor roosts had fewer than 100 in total over the ten-year period while major roosts had more than 100,000.

The “vulnerable” listing means the species is at risk of extinction. But it’s not as dire as if it were “endangered”.

The original vulnerable assessment[7], endorsed in 2001, was based on a population decline of about 30% over ten years and the potential for ongoing land clearing in the grey-headed flying fox’s core range.

But this is the flying fox you’re most likely to see and hear in south-east Australia, from Sydney to Adelaide.

During the day, flying foxes like to hang out together. They rest and socialise in large roosts, sometimes numbering more than 100,000 animals.

A large group of grey-headed flying foxes roosting in a tree More than 150,000 grey-headed flying foxes roosted in Gympie, Queensland, after much of their habitat burned during the Black Summer of 2019-20. Eric Vanderduys, CSIRO

As the sun sets, they take to the sky, departing in large streams to forage during the night in the surrounding landscape. They can travel long distances to find food, sometimes venturing more than 40km from home, and flying more than 300km in a single night.

Their food of choice is nectar from a wide variety of eucalypt, bloodwood and melaleuca species. In return, they play an important pollination role, as if they were nocturnal bees with a one-metre wingspan.

They also feed extensively on native figs. In urban areas, they feast on the nectar and fruit of introduced species found in gardens and street trees[8].

Individuals regularly change roosts. They move throughout the species’ range[9], following food resources.

That means the number of bats in roosts is constantly changing, depending on the availability of the surrounding resources, which makes accurate counting particularly challenging.

A grey-headed flying-fox hanging from a tree, wrapped in its wings, with its eyes wide open Grey-headed flying foxes sleep and socialise during the day but are often well aware of approaching humans. Adam McKeown, CSIRO

Monitoring a threatened species

Australia’s national science agency, CSIRO, co-ordinated the National Flying-fox Monitoring Program in partnership with federal and state environmental agencies from 2012 to 2022.

The intention was to monitor the populations of the two nationally listed flying fox species on the mainland. It was specifically designed to understand their population trends. Here we focus on the grey-headed flying foxes.

The program involved quarterly visits by federal, state and local government staff and volunteers to as many flying fox roosts as possible. Over the entire program almost 12,000 counts were conducted at 912 potential roosts. Grey-headed flying foxes were found at 469 of those roosts.

This program would not have been possible without hundreds of hours of work around the clock by staff and volunteers, often in challenging conditions. Their work highlights the importance of long-term monitoring programs.

From 2012 to 2022 we counted an average of 580,000 grey-headed flying foxes in each survey. But total numbers ranged between 330,000 and 990,000, with strong seasonal variation. This variation relates to their reproductive cycle and the availability of food within their range.

Flying foxes pup late in the year. When those pups become independent, they can be counted. This results in a sudden increase in the numbers, typically around February. So while our data show peaks and troughs throughout each year, overall the population remained stable.

We developed a model to allow for this seasonality and examine overall population trends. The model strongly suggests the population hovered around 600,000 adults for the ten years of the survey. We found a 70% chance of a slightly increasing population, versus a 30% chance the population has declined slightly.

The population appeared to be stable despite exceptional events such as the 2019–20 megafires[10] and severe heatwaves known to have killed thousands of flying foxes[11].

The flying foxes seem resilient to these threats for two main reasons.

First, they are nomadic and well adapted to travelling long distances. This allows them to evade threats such as fires and droughts.

Second, grey-headed flying-foxes are likely to benefit from a “human-modified landscape[12]”. In other words, they may well be urban “winners”, as the urban areas we’ve created provide diverse foraging opportunities.

Grey-headed flying foxes continually occupied[13] all major cities within their range throughout our monitoring program.

These urban environments offer a smorgasbord of flowering and fruiting species, especially palms and figs. Many of these species are exotics, with flowering and fruiting patterns that flying foxes can readily exploit.

We found continuous occupation of individual roosts was unusual. The few that were continuously occupied were all in urban areas, supporting the view that urban areas are increasingly important[14] for this species.

Closeup of a young grey-headed flying fox looking at the camera, with a dark green leafy background This young grey-headed flying fox is big enough to count. Eric Vanderduys, CSIRO

Good news, but we need to be cautious

After ten years of monitoring we can safely say the grey-headed flying fox is doing ok, for the time being.

But threats to its survival remain. Climate change is expected to cause more heatwaves[15], bushfires and droughts within their range. This could turn their fate around.

It’s also worth noting that while our monitoring continued for two years after the 2019–20 bushfires, the longer-term impacts are still unknown.

Given this uncertainty, continuing monitoring using similar methods and incorporating updated technology would increase certainty about the population trajectory. Unfortunately, monitoring has paused since 2022, pending further funding discussions.

Read more: To stop new viruses jumping across to humans, we must protect and restore bat habitat. Here's why[16]

References

  1. ^ our decade-long survey (doi.org)
  2. ^ National Flying-fox Monitoring Program (www.dcceew.gov.au)
  3. ^ Black Summer of 2019–20 (recovery.preventionweb.net)
  4. ^ Flying foxes pollinate forests and spread seeds. Here's how we can make peace with our noisy neighbours (theconversation.com)
  5. ^ grey-headed flying fox (www.environment.gov.au)
  6. ^ established in South Australia (www.environment.sa.gov.au)
  7. ^ vulnerable assessment (www.dcceew.gov.au)
  8. ^ gardens and street trees (journals.plos.org)
  9. ^ species’ range (link.springer.com)
  10. ^ 2019–20 megafires (theconversation.com)
  11. ^ severe heatwaves known to have killed thousands of flying foxes (theconversation.com)
  12. ^ human-modified landscape (doi.org)
  13. ^ continually occupied (www.environment.gov.au)
  14. ^ urban areas are increasingly important (www.publish.csiro.au)
  15. ^ heatwaves (www.acs.gov.au)
  16. ^ To stop new viruses jumping across to humans, we must protect and restore bat habitat. Here's why (theconversation.com)

Read more https://theconversation.com/grey-headed-flying-fox-population-is-stable-10-years-of-monitoring-reveals-this-threatened-species-is-doing-well-226319

Times Magazine

Headless CMS in Digital Twins and 3D Product Experiences

Image by freepik As the metaverse becomes more advanced and accessible, it's clear that multiple sectors will use digital twins and 3D product experiences to visualize, connect, and streamline efforts better. A digital twin is a virtual replica of ...

The Decline of Hyper-Casual: How Mid-Core Mobile Games Took Over in 2025

In recent years, the mobile gaming landscape has undergone a significant transformation, with mid-core mobile games emerging as the dominant force in app stores by 2025. This shift is underpinned by changing user habits and evolving monetization tr...

Understanding ITIL 4 and PRINCE2 Project Management Synergy

Key Highlights ITIL 4 focuses on IT service management, emphasising continual improvement and value creation through modern digital transformation approaches. PRINCE2 project management supports systematic planning and execution of projects wit...

What AI Adoption Means for the Future of Workplace Risk Management

Image by freepik As industrial operations become more complex and fast-paced, the risks faced by workers and employers alike continue to grow. Traditional safety models—reliant on manual oversight, reactive investigations, and standardised checklist...

From Beach Bops to Alpine Anthems: Your Sonos Survival Guide for a Long Weekend Escape

Alright, fellow adventurers and relaxation enthusiasts! So, you've packed your bags, charged your devices, and mentally prepared for that glorious King's Birthday long weekend. But hold on, are you really ready? Because a true long weekend warrior kn...

Effective Commercial Pest Control Solutions for a Safer Workplace

Keeping a workplace clean, safe, and free from pests is essential for maintaining productivity, protecting employee health, and upholding a company's reputation. Pests pose health risks, can cause structural damage, and can lead to serious legal an...

The Times Features

Distressed by all the bad news? Here’s how to stay informed but still look after yourself

If you’re feeling like the news is particularly bad at the moment, you’re not alone. But many of us can’t look away – and don’t want to. Engaging with news can help us make ...

The Role of Your GP in Creating a Chronic Disease Management Plan That Works

Living with a long-term condition, whether that is diabetes, asthma, arthritis or heart disease, means making hundreds of small decisions every day. You plan your diet against m...

Troubleshooting Flickering Lights: A Comprehensive Guide for Homeowners

Image by rawpixel.com on Freepik Effectively addressing flickering lights in your home is more than just a matter of convenience; it's a pivotal aspect of both home safety and en...

My shins hurt after running. Could it be shin splints?

If you’ve started running for the first time, started again after a break, or your workout is more intense, you might have felt it. A dull, nagging ache down your shins after...

Metal Roof Replacement Cost Per Square Metre in 2025: A Comprehensive Guide for Australian Homeowners

In recent years, the trend of installing metal roofs has surged across Australia. With their reputation for being both robust and visually appealing, it's easy to understand thei...

Why You’re Always Adjusting Your Bra — and What to Do Instead

Image by freepik It starts with a gentle tug, then a subtle shift, and before you know it, you're adjusting your bra again — in the middle of work, at dinner, even on the couch. I...