In short
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Sleeping Koala - photo by Justin Cally.
Koalas in Victoria
Koalas are an iconic Australian animal and their conservation status varies across the country. In New South Wales, Queensland, and the Australian Capital Territory, Koalas are officially listed as endangered. In contrast, some populations in Victoria and South Australia have reached unsustainable densities, causing overbrowsing of preferred eucalypt trees, which requires ongoing management.
Despite the pockets of overabundance, concerns remain about the population health of Koalas in Victoria. Following the near statewide extinction of the species in the early 1900s, Koalas were reintroduced to parts of Victoria through translocations from small, isolated populations in the 1940s. While this helped restore numbers, it may have had lasting impacts on the genetic diversity of today’s population.
Genetic diversity has broad implications for how Victoria’s Koala population can respond to disease, climate change, or other stressors. To ensure the future of Victoria’s Koalas, we need a clearer picture of their population size, genetic health, and disease prevalence.
What we’re doing
ARI has delivered Victoria’s first comprehensive statewide Koala survey in partnership with Deakin University, Federation University, University of Queensland and University of Melbourne. This research assessed the abundance, genetics and health of Koalas to understand the potential threats and develop baseline data on the status of Victora’s Koala population.
Koala - photo by Justin Cally
The project delivered three components:
- Population surveys: comprehensive field surveys were conducted to estimate Koala numbers and distribution across public lands and eucalypt plantations in Victoria.
- Genetic analysis: targeted genetic sampling to examine the genetic diversity and population structure of Victoria’s Koalas.
- Health and welfare assessments: targeted assessments to collect baseline data on Koala health and disease prevalence.
Koala surveys
Koala surveys were undertaken in 2023 and 2024 at 182 sites. The surveys used ground-based counts using line transect distance sampling in suitable habitat and acoustic monitoring to measure Koala presence. Acoustic monitoring uses passive acoustic recorders to help detect Koalas in areas with low population density, where Koalas might be missed by ground searches.
By combining Koala records and environmental variables, such as the presence of eucalypt food trees, temperature, rainfall, soil moisture and elevation, we constructed a statistical model to estimate the density of Koalas across Victoria. This model allowed us to estimate the total number of Koalas on public land and in plantations across Victoria.
Key findings:
- In 2024, Victoria’s Koala population was estimated at 225,000 individuals (90% credible interval: 181,300 – 276,600].
- Almost half of Victoria’s Koala population was found within Victoria’s South-West region.
- Koalas are estimated to occupy ~34% of their modelled potentially suitable habitat in Victoria.
- Koala densities were higher in moist areas with flatter terrain, less variable climate extremes, and higher amounts of vegetation, where the leaves they feed on might hold a higher moisture content.
- 51,700 Koalas resided in the hardwood plantation estate.
- Koala density was found to be more than 6 times higher in Blue Gum (Eucalyptus globulus) plantations than in the neighbouring native forest in southwest Victoria.
Estimated distribution of Koalas during the 2024 survey.
Recommendations:
- Regular Statewide Monitoring: Run population surveys every 5 years to track statewide trends.
- Informed Plantation Management: Koala management should consider information on plantation age and rotation for Victoria’s Blue Gum plantation estate due to high numbers of Koalas in plantations.
- Post-Harvest Impact Studies: Investigate the welfare outcomes of Koalas living in Blue Gum plantations following plantation harvest.
Genetic analysis
Koala blood, tissue and scat samples were analysed by Diversity Arrays Technology to map the genetic structure of Victoria’s Koala populations. This allowed us to understand the population’s genetic diversity, movement of animals between populations and boundaries of subpopulations.
Key findings:
- Victorian Koalas are genetically vulnerable, with low adaptive potential to face emerging threats and future climates.
- Victoria’s Koalas have less genetic diversity than QLD and NSW populations.
- The Victorian Koala population is characterised by three main genetic clusters: one well-defined remnant population (South Gippsland) and two clusters that are intermixed, potentially representing ancestry from Koalas translocated from Phillip and French Islands.
- The South Gippsland cluster, including populations from Wilson’s Promontory, had the highest genetic diversity in the state.
- Eastern populations of Gelantipy and Mallacoota had the highest inbreeding and lowest diversity in the state.
- Koala effective dispersal distance was estimated to be low, with most dispersal occurring within 10km, with maximum dispersal distances of 25km.
Map of the genetic clusters of Koala in Victoria.
Recommendations:
- Addressing inbreeding risks: Genetic management is needed for Koala populations identified as having a high risk of inbreeding depression (e.g. Ballarat, Murray River, Mallacoota) to increase genetic diversity.
- Informed translocation programs: Population viability analysis should be conducted to understand the long-term outcomes of any planned translocation program to improve genetic diversity.
- Genetic recovery: To improve genetic diversity in Victorian Koalas, translocations from the South Gippsland genetic cluster or NSW populations could be considered.
Health and welfare assessments
Detailed clinical health assessments and targeted disease surveillance were conducted on 68 Koalas captured from seven locations across the state. All assessments were conducted by an experienced wildlife veterinarian.
The locations for detailed health assessments were selected based on existing knowledge of Koala genetics and disease issues, and the need to improve or supplement existing understanding of Koala health.
Key findings:
- Higher than expected rates of chronically poor health and welfare were found across several Koala populations, raising concerns for the overall health of Victoria’s Koalas.
- 39 (57%) Koalas were considered healthy and released, while 29 Koalas (43%) were found to be in chronically poor health and were euthanised on welfare grounds.
- Koalas in poor health were more likely to have poor coat condition, dental disease, and ‘wet bottom’, and were more likely to occur in areas with high Koala densities.
- Infectious organisms were detected in 59% of Koalas; Chlamydia percorum DNA was detected in 43% of Koalas, and Koala Retrovirus was detected in 23% of Koalas.
- Dental disease was recorded in 37% of Koalas across all age classes and regions, except Mallacoota, with just over half of all cases associated with dental malocclusion.
Recommendations:
- Investigating root causes: Ongoing research is needed to better understand the underlying causes of poor health across Koala populations in the state.
- Centralised health data repository: Establishing a comprehensive repository for Koala health records, biological samples, and DNA will support more coordinated research and conservation efforts.
- Managing high-density populations: areas of overabundant Koalas need management strategies to be evidence-based and regularly reviewed to ensure they meet both conservation and animal welfare goals.
Koala after assessment - photo by Justin Cally
Publications and resources
- ARI Technical Report 393 - The status of Victoria’s Koala population (2025) (PDF, 4.66 MB) (DOCX, 3.6 MB)
- ARI Technical Report 272 - Towards a habitat condition assessment method for guiding the management of overabundant Koala populations (PDF, 1.0 MB) (DOCX, 1.4 MB)
- Koala translocation (ARI webpage)
- A History of Koala management in Victoria (book chapter)
Acknowledgements
This project was funded by the Department of Energy, Environment and Climate Action (DEECA) under the Victorian Koala Management Strategy.
We would also like to thank the many local property owners, Landcare, Friends groups and wildlife shelter volunteers whose assistance with the project was invaluable.
Koala and joey - photo by Justin Cally
Page last updated: 09/09/26