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Using Passive Acoustic Monitoring (PAM) and Localisation Methods to Study Low-Density Koala Populations in North Queensland

Updated: May 27

The distribution of koala populations in North QLD is poorly known. An improved understanding of the distribution and abundance of these “tropical” koalas may help us better manage the landscapes that support them.


Project led by Roger Martin


Roger Martin setting up a BAR-LT on Yourka Reserve (Photo: Miranda Fittock)
Roger Martin setting up a BAR-LT on Yourka Reserve (Photo: Miranda Fittock)

Wildlife Biologist Roger Martin, with the aid of wildlife veterinarian Amy Shima and the team from Yourka Reserve (Bush Heritage Australia), use bioacoustic methods to increase our understanding of these previously unstudied northern koala populations. This will provide crucial information to help conserve them against future threats.


Project Overview


Despite the iconic status of koalas, in Australia and globally, surprisingly little is known about distribution and behaviour in North Queensland, the tropical limit of their range. According to wildlife biologist Roger Martin, co-author of ‘The Koala: Natural History, Conservation and Management’, most research effort has focused on southerly populations, near major cities such as Brisbane, Sydney and Melbourne, a result of funding availability and public interest. Understanding koala distribution, especially at the extremes, is crucial to inform efforts to protect them.


An additional challenge to research on northern populations is their much lower density compared to their southern counterparts. Even in situations of abundance, individual koalas are hard to find. Studying populations at low abundance has proven to be very difficult. Fortunately, bioacoustic methods are proving to be the key.


‘…the work I did down south, we didn’t think so much of the significance of koala vocalisations because they’re very high abundance populations. Up here, it’s key to understanding their biology. How do male and female find each other to mate during the breeding season when they’re probably ranging over 5000 hectares of habitat? It’s from vocalisations, not just happenstance.’ -Roger


Athi the koala that Roger and Amy have been monitoring for several years on the Atherton Tablelands (Photo: Miranda Fittock)
Athi the koala that Roger and Amy have been monitoring for several years on the Atherton Tablelands (Photo: Miranda Fittock)

Roger has worked with koalas since 1977 and knows them like the back of his hand. He has used all manner of monitoring methods over the years but has recently adopted PAM (Passive Acoustic Monitoring) to replace traditional approaches to detection. The advantages of PAM over camera traps and in-field surveys are the ability to sample greater area, for longer periods and at less effort. PAM is beginning to answer questions on presence / absence (at high confidence) and, perhaps, abundance. An additional advantage of PAM is minimal disturbance to study animals and the landscape as well as the potential to provide information on behaviour and movement. It has already proven highly useful at gathering information on other threatened species such as yellow-bellied glider (Petaurus australis).


Roger is determined to learn more about koala distribution in light of massive land use changes occurring in the region. He is concerned that the transition to renewable energy in Australia has seen a surge in wind farm construction along the Great Dividing Range, including northern Queensland. While moving away from fossil fuels is a step toward reduced carbon emissions, the reality is there too few restrictions as to where wind farms can be deployed, says Roger.


‘The EPBC Act, which is the main environmental act in Australia, was promulgated in 1999 and at that time there were no wind farms in Australia, so there are no regulations about siting, setback distances, or putting them high biodiversity areas.’ -Roger

Wind farm near Ravenshoe
Wind farm near Ravenshoe

Many of the chosen sites for new wind farms will impact the few remaining high biodiversity areas, including viable habitat for koalas. The biodiversity impacts of wind farm projects include extensive land-clearing associated with the necessary road infrastructure and, peculiarly, low frequency sound (produced by turbines) that can travel great distance. This low frequency sounds overlaps that of koala bellows and may mask their calls in a landscape.


‘Most of the restrictions and setbacks are usually to do with people rather than wildlife. But wildlife is a lot more sensitive to low frequency sounds than people are.’ -Roger


The monitoring underway, by Roger and his colleagues, will help to establish a base line picture of koala populations so that various impacts can be properly assessed.


‘...a lot of wind farms here are going into very high biodiversity areas which are also modelled as being koala refuge habitat if the temperatures go up another two degrees or so. So that’s very poor form, we need to pick up our game.’ -Roger


BAR-LTs in the field at Yourka Reserve (Photos: Miranda Fittock)


METHODS


Study area- Yourka Reserve


Yourka Reserve (Yourka | Bush Heritage Australia), previously used for beef cattle production, was restored by Bush Heritage Australia. It now provides 43,500 ha of high-quality habitat for native wildlife. The property harbours a diversity of Eucalyptus species, including gum-topped box, poplar gums and blue gums (favourite food species of koalas). Given the availability of reliable water and food trees in the area as well as previous sightings and traces of koalas (scat and scratch marks), Roger deemed the reserve as an ideal area for a population study.


Yourka Reserve (Photos: Miranda Fittock)


Recording schedule, settings and set up


Koalas are most active between the hours of dusk and dawn, with vocalisations at frequencies ranging from 20 to 900 Hz. With this in mind, the PAM recorders (Frontier Labs BAR-LT) were equipped with low frequency microphones and scheduled to record continuously between dusk and dawn for two weeks. The recorders were programmed with special localisation software pre-deployment. Microphone gain was set to 50dB and the recordings were made at a sampling rate of 44.1 kHz.


Roger and the team prepping for deployment (Photos: Miranda Fittock)


Device Deployment


Twenty-one BAR-LT recorders were deployed at Yourka Reserve in late November 2024, with the assistance of reserve staff (Christine and Macey), timed to encompass the koala breeding season (August–February). The recorders were arranged in three rows of seven, running parallel to a creek (see diagram below). Each recorder was spaced 200 m apart, forming an approximate 1 km² array. A 200 m spacing was selected on an estimated propagation distance of koala bellows (~600 metres) through forested habitat, beyond which distance signal strength significantly diminishes.

Project deployment diagram for the 21 BAR-LTs arranged within an approximate 1 km² array, positioned specifically for localisation with devices pre-programmed with localisation software.
Project deployment diagram for the 21 BAR-LTs arranged within an approximate 1 km² array, positioned specifically for localisation with devices pre-programmed with localisation software.

What comes next?


Since the initial deployment in November, Roger and Amy conducted a second deployment at Yourka Reserve in January 2025, at the same site. Now that all recorders have been retrieved, the next step is to dive into the data. With hundreds of hours of recordings to sort through, it’s a daunting task-but Roger is hopeful that recognisers will help streamline the process and save countless hours of manual analysis. We’ll be sharing updates on this blog and our social media, so stay tuned!


Deployment of BAR-LTs at Yourka Reserve, Einasleigh Uplands, North Qld (Photos: Miranda Fittock)



Researcher Bio


Roger Martin is a long-standing and highly respected figure in the field of koala research. Having worked with koalas since 1977, he has made significant contributions to our understanding of the species through extensive field observations across Australia. He is the co-author of The Koala: Natural History, Conservation and Management (with Kathrine Ann Handasyde) and has published numerous scientific papers on koala behaviour, population dynamics, morphology, and more. He now leads the Tree-Kangaroo and Mammal Group’s koala project alongside wildlife veterinarian Dr Amy Shima. Together, they survey koala populations in the Atherton Tablelands as part of the National Koala Monitoring Program.


Roger standing before an impressive termite mound on Yourka Reserve after a morning spent deploying BAR-LTs (Photo: Miranda Fittock)
Roger standing before an impressive termite mound on Yourka Reserve after a morning spent deploying BAR-LTs (Photo: Miranda Fittock)

Words and images supplied by Miranda Fittock


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