From 60 to 1.7 Million: How the Red Fox Conquered Australia in Just 60 Years

When European settlers of British origin brought the red fox (Vulpes vulpes) to Australia from around 1870 onward, they were thinking of tradition, not ecological consequences. Hunting foxes with packs of hounds, then a deeply rooted social ritual in England and now banned, was meant to continue in the new homeland. No one suspected that this hunting tradition, a symbol of colonial leisure culture, would throw the ecological balance of an entire continent off course.

Within a few decades, the foxes spread across southern and eastern Australia, highly adaptable, without natural enemies, and with abundant prey. For many native marsupials that had lived for millennia without larger ground-dwelling predators, a struggle for survival began, and they lost it.

In 1927, the Australian zoologist Hedley Herbert Finlayson wrote about the toolache wallaby (Notamacropus greyi):

“In the almost uninhabited desert regions where humans scarcely intervene, the fox seems to have been the sole agent of extermination.”

Finlayson saw the predator as the destroyer of numerous species. Later researchers such as Tim Flannery partly qualified this view, but the damage had long been obvious. The introduced red fox had become an ecological force that reached even remote regions.

The pattern repeated itself again and again: the desert rat-kangaroo (Caloprymnus campestris), the desert bandicoot (Perameles eremiana), or the lesser bilby (Macrotis leucura) disappeared in the 20th century, and almost always the red fox was partly responsible.

Together with feral cats and rabbits, also introduced by Europeans, it transformed entire ecosystems: it ate juveniles, displaced native predators, and intensified the overgrazing of the landscape through rabbit plagues.

The red fox in Australia: an invasion in record time

How quickly the red fox actually spread is shown by a recent study by Sean Tomlinson et al. (2025). Researchers at the University of Adelaide combined historical documents, newspaper reports, and hundreds of first sightings with modern, process-based models. This allowed them for the first time to reconstruct the fox invasion across the Australian continent with high spatial and temporal resolution.

The result: Just 60 years were enough to occupy almost the entire potential range. Starting from three introduction sites, Werribee, Corio, and Ballarat in the state of Victoria, the fox spread rapidly east and south from 1870 onward. By around 1895, southeastern Australia had been fully colonized. Between 1900 and 1930, the species expanded into the dry inland regions of central and western Australia, slowed by lower rainfall. By about 1940, foxes had finally also reached the west, northwest, and northeast of the continent.

Later releases, for example in Goulburn (1895) or on the Yorke and Eyre peninsulas (1901/1902), changed little. The first roughly 60 animals near Geelong were enough to trigger a continent-wide invasion. Today, an estimated 1.7 million red foxes live in Australia, almost everywhere except for some tropical regions in the north.

How researchers reconstructed the fox’s spread

To understand how the red fox spread across Australia, Sean Tomlinson’s team used so-called spatially explicit population models (SEPMs). These models link ecological data such as climate, land use, and habitat quality with biological characteristics of the species, for example how quickly foxes reproduce, how far they wander, and how dense their populations can become.

In more than 50,000 simulations, the researchers varied these parameters and then compared the results with historical sources, including newspaper reports, records of fox hunts, and first sightings. In this way, a detailed picture emerged showing when and where foxes actually spread, year by year and region by region.

Key results of the model:

• Habitat quality: Agriculture and settlements provided abundant food; foxes found ideal conditions there for spreading.
• Population density: Up to 10 animals per square kilometer, especially in moist, agriculturally used regions.
• Rate of spread: On average around 30 kilometers per year, in individual cases up to 200 kilometers.
• Founding population: About 60 animals were enough to colonize all of Australia in the long term.

After the Second World War, populations in agriculturally used regions increased sharply again, in parallel with the ongoing expansion of cropland. Field studies show: the more intensive the land use, the higher the fox density. Agriculture and predation thus acted together as the main drivers of species decline.

The foxes’ recipe for success

Why was the red fox able to spread so rapidly across Australia and establish itself permanently? Several ecological and human factors worked together and created perfect conditions for the invader.

• Lack of natural enemies
  In Australia, the fox encountered little resistance. Only where dingoes (Canis dingo) occur, introduced by humans about 3,500 years ago but now a fixed part of the ecosystems, are fox densities noticeably lower. Dingoes act as a natural control: they hunt foxes or drive them from their territories. Without this competition, the invasive predator was able to spread unhindered.
• High adaptability
  Red foxes are true survival artists. They cope in almost any habitat, in forests, open agricultural landscapes, semi-deserts, and even cities. As omnivores, they use every available food source: carrion, fruit, small animals, or waste. This enormous flexibility quickly made them successful in the unfamiliar environment.
• Climatic tolerance
  The animals thrive in both humid and dry regions. In agriculturally used areas with higher rainfall, they reach their highest densities because the food supply is especially abundant there. Surprisingly, however, the models showed that growth rates in arid zones were at times higher, an indication of their ability to adapt rapidly to extreme conditions and irregular resources.
• Human-driven landscape change
  Agriculture, grazing, and settlement created a mosaic of open spaces in which foxes could hunt more easily. These human-altered landscapes offered ideal conditions for explosive population growth, especially after the Second World War.

Consequences for native wildlife

The effects on Australia’s unique wildlife were devastating. Red foxes hunted not only small marsupials but also ground-nesting birds and reptiles, causing damage in almost all ecosystems. Juveniles in particular were easy prey.

The victims include the greater bilby (Macrotis lagotis), which is now highly threatened, and the pig-footed bandicoot (Chaeropus ecaudatus), which disappeared no later than the middle of the 20th century, probably through predation by introduced foxes and feral cats as well as the destruction of its habitat by livestock grazing.

The red fox’s “success story” in Australia is emblematic of a global pattern: the human-caused spread of invasive species is now one of the greatest threats to global biodiversity. What began in Australia is repeating itself in countless regions, often with the same mechanisms and consequences.

Global parallels: invasive species as a worldwide problem

European colonization of Australia from 1788 onward triggered a cascade of ecological changes whose consequences are still visible today. According to Andrew A. Burbidge (2024), more than 40 mammal species have gone extinct in Australia since then, more than on any other continent.

Both the red fox and feral domestic cats, both introduced by European settlers, are considered by a study by John Woinarski et al. (2015) to be the main drivers of numerous extinctions and range losses among Australian vertebrates. Added to this are altered fire regimes and the conversion of natural vegetation into agricultural landscapes, which further increase the pressure on native fauna.

But Australia is not an isolated case, it stands as an example of a worldwide phenomenon. According to the IPBES report (2023), invasive species are now among the five main causes of global biodiversity loss. They are involved in about 60% of all documented extirpations, and in 16% they are even the sole cause. Worldwide, more than 37,000 non-native species have established themselves, and at least 3,500 of them are considered invasive. Island ecosystems are especially sensitive: ground nesters, flightless birds, and specialized small mammals there have hardly any defense strategies against new predators.

Well-known examples illustrate the scale of the problem: the Maclear’s rat (Rattus macleari) disappeared after the introduction of the black rat (Rattus rattus), which transmitted pathogens and directly competed with the native species. The Christmas Island pipistrelle (Pipistrellus murrayi), by contrast, fell victim to a combination of several introduced species, above all rats and feral cats, but probably also snakes and invasive ants, which heavily affected its habitats and prey. The Stephens Island wren (Traversia lyalli) from New Zealand’s Stephens Island was ultimately exterminated by introduced cats.

In Australia too, different threats acted together: foxes and cats hunted marsupials, rabbits destroyed vegetation through overgrazing, livestock compacted the soil, and altered fire regimes further destabilized habitats. This complex interaction continues to this day, and it makes clear how human interventions can permanently alter ecological balances.

The case of the red fox in Australia thus symbolizes a global pattern: human mobility, trade, and climate change accelerate the spread of invasive species, and with it species loss worldwide.

Lessons for conservation

The most important lesson is this: prevention is the most effective conservation. The earlier a biological invasion is recognized and stopped, the lower the ecological and economic damage.

To prevent future catastrophes, several interlocking measures are needed:

• Strict border controls and biosecurity measures to prevent the introduction of new species.
• Targeted control of invasive predators in protected areas, for example through baiting programs, trapping, or the creation of large predator-proof zones.
• Restoring natural predators such as the dingo, whose populations have been heavily reduced since European settlement. Because it was seen as a “sheep killer,” it was systematically persecuted, poisoned, and fenced out of vast areas for decades. Yet as an apex predator, the dingo performs a central ecological function: it keeps foxes and feral cats in check, limits overabundant prey animals such as kangaroos, and thus helps stabilize entire ecosystems.
• Modern monitoring technologies such as environmental DNA (eDNA), acoustic monitoring, and AI-supported modeling that can detect the spread of invasive species at an early stage.

Australia is now considered a pioneer in invasive-species management. Projects such as predator-free zones, eDNA analyses, and nationwide control programs against foxes and cats show that determined action can succeed. In several states, large fenced protected areas have been created, and on many Australian islands threatened species such as the bilby, the rufous hare-wallaby (Lagorchestes hirsutus), or the numbat (Myrmecobius fasciatus) have also been successfully reintroduced.

The modeling approach from the current study offers a valuable tool: it can help reconstruct the spread of other invasive species, for example feral domestic cats, with spatial and temporal precision. Such data-based methods improve not only our understanding of past invasions, but also provide the basis for recognizing and stopping future threats at an early stage. If these findings are implemented consistently, it may be possible to prevent the story of the red fox, or that of a new invasive species, from repeating itself.

When a few become millions

The history of the red fox in Australia shows how few individuals are enough to throw an entire ecosystem out of balance. From around 60 introduced animals, a population of more than 1.7 million emerged within a century, with devastating consequences for numerous endemic species.

The new study by Tomlinson et al. provides high-resolution data for the first time that make the connection between the spread of the red fox and regional extinction events visible. It shows where and when invasive predators do the greatest damage, and thus offers a scientific basis for managing these hotspots more specifically in the future.

At the same time, the research makes clear how crucial modern methods are for conservation. Models like this one make it possible not only to understand biological invasions in retrospect, but also to predict future developments. The red fox invasion is therefore more than a chapter in Australian colonial history; it is a warning to act in time before a few animals become millions.

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Sources & further reading

• Burbidge, A. A. (2024). Australian terrestrial mammals: how many modern extinctions? Australian Mammalogy. https://doi.org/10.1071/AM23037
• Finlayson, H. H. (1927). Observations on the South Australian members of the subgenus Wallabia. Transactions of the Royal Society of South Australia, 51, pp. 363–377. https://www.biodiversitylibrary.org/item/129843#page/1/mode/1up
• IPBES (2023): Thematic Assessment of Invasive Alien Species and Their Control. https://www.ipbes.net/IASmediarelease
• Tomlinson S., Brown, S. C., Haythorne, S. et al. (2025): Reconstructing Fox Invasion of Australia: A Process-Based Approach Using Historical Sightings. Diversity and Distributions, 31(10), e70095. https://doi.org/10.1111/ddi.70095
• Woinarski, J. C. Z. et al. (2015): Ongoing unraveling of a continental fauna: Decline and extinction of Australian mammals since European settlement. PNAS, 112(15), 4531–4540. https://doi.org/10.1073/pnas.1417301112