Too Many Koalas: South Australia’s Booming Koala Population Is Destroying Its Own Habitat — Scientists Warn of Looming Ecological Collapse

A Conservation Win That Became Its Own Disaster

South Australia's koalas were once on the brink. Decades of habitat clearing, disease, and hunting had reduced populations across the country to critically low levels, prompting intensive conservation efforts, including wildlife reserves, habitat restoration, and legal protections. Those efforts worked — perhaps too well in one region. A new study published in Ecology and Evolution (January 2026) and widely highlighted by ScienceDaily on June 8, 2026, warns that South Australia's koala population in the Mount Lofty Ranges has grown so large that it is now destroying the very habitat that sustains it — putting the animals at risk of widespread starvation and long-term ecological collapse if urgent management action is not taken.

The research, led by Dr. Frédérik Saltré of the University of Technology Sydney and the Australian Museum, with researchers from Flinders University and the University of Wollongong, provides the first comprehensive population estimate for the region. Their findings show that the Mount Lofty Ranges koala population currently represents approximately 10% of Australia's entire koala population — an extraordinary concentration for a single geographic area. And without intervention, the researchers project it could grow by a further 17 to 25% over the next 25 years, accelerating the strain on food supply, vegetation, and native habitat.

The Paradox of Abundance: How Overpopulation Threatens a Protected Species

Koalas are specialist feeders: they subsist almost entirely on eucalyptus leaves, consuming large quantities each day. In a balanced ecosystem, koala populations are kept in check by predators, disease, and habitat limits. But in the protected, fragmented landscapes of the Mount Lofty Ranges — where dingoes are absent and habitat corridors limit natural dispersal — koala numbers have grown unchecked. The result is browse pressure: koalas defoliate their preferred eucalyptus trees faster than the trees can regrow, progressively stripping the forest of the food source it depends on.

Using advanced spatial modelling and data from thousands of citizen science observations, the researchers found koala densities in many areas that are above what the South Australian government considers sustainable. The historical precedent is grim: at Cape Otway in Victoria, a koala population boom in the early 2010s stripped the region's manna gum woodland, leading to mass starvation and total population collapse. The researchers warn that South Australia may be heading toward the same trajectory without proactive intervention.

A Humane Solution — and the Study's Limitations

The researchers are not calling for culling. Their study specifically tested the efficiency and cost-effectiveness of targeted fertility control as a humane, science-based approach to population stabilization. By modeling different sterilization scenarios — targeting specific age groups, geographic hotspots, or population density thresholds — the team identified strategies that could prevent population overshoot while avoiding lethal intervention. The South Australian Department for Environment and Water funded the research, reflecting government commitment to finding a practical management pathway. Dr. Katharina Peters of the University of Wollongong stated: "Nobody wants to see koalas being culled or starved because their habitat cannot sustain their numbers. That's why it's so important to manage the population and prevent it from becoming too large."

The study does have important limitations. The population estimates rely on citizen science observations, which, while extensive, may not uniformly sample all parts of the range. Spatial modelling involves assumptions about habitat quality and koala carrying capacity that future field surveys could refine. The effectiveness of fertility control programs in wild koalas — while proven in principle — has not yet been tested at the scale the study recommends, and implementation costs and logistical challenges at landscape scale remain substantial.

The broader lesson from this research applies well beyond Australia. Conservation success can create its own challenges when species recover faster than their ecosystems can accommodate — particularly in fragmented, human-modified landscapes where natural population regulators have been removed. Science-based, humane, and anticipatory management frameworks — like the one this study proposes — are increasingly essential tools for conservation in the modern world. And the time to apply them is before the crash, not after.