In 1859, 24 Rabbits Were Released In Australia — Within 90 Years There Were 600 Million — A Biologist Explains
In 1859, Thomas Austin introduced European rabbits to Australia for sport, inadvertently unleashing an ecological disaster. From just two dozen, their population exploded to hundreds of millions by the mid-20th century, becoming one of the fastest colonizations by an introduced mammal. This rapid spread was due to Australia lacking the rabbits' natural predators, parasites, and harsh winters, allowing unchecked reproduction. The resulting overgrazing and erosion devastated native ecosystems. Australia implemented biological controls like myxomatosis and rabbit hemorrhagic disease viruses, which initially reduced numbers but faced evolutionary resistance. This saga underscores the critical importance of biosecurity for vulnerable ecosystems.
In October 1859, a settler named Thomas Austin had a crate of European rabbits shipped to his estate near Geelong, Australia, so he and his friends could shoot them for sport.
A mixed shipment of wild and domestic stock — about two dozen animals, by the most common account — went into the paddock. Within a decade, rabbits on Austin’s property alone numbered in the tens of thousands, and the population kept radiating outward across the continent.
By the early 1900s the population had already exploded into the tens of millions across the southern half of the continent. The number most often quoted for the plague’s peak — 600 million — actually comes from decades later, in the late 1940s, when a run of wet years and wartime disruption to fencing and trapping let the population balloon further; contemporary counts from any era, though, are necessarily rough.
Either way, it stands as one of the fastest colonizations of a new landmass by an introduced mammal ever documented.
To a biologist, the number itself is’’t the surprising part; rabbit reproduction is famously explosive. A female European rabbit can conceive again within a day of giving birth, a trait called postpartum estrus, as recorded in Animal Diversity Web, a zoological database maintained by the University of Michigan, and reaches sexual maturity within months. Multiply a handful of litters a year, each with several young, by a population with almost no losses, and the growth curve goes exponential fast.
What made Australia different from the rabbit’s native range wasn’t the math, it was the missing constraints. Ecologists call this the enemy release hypothesis, a framework formalized in a 2002 study published in Trends in Ecology & Evolution: when a species is introduced to a new region without the predators, parasites and diseases that kept it in check back home, its population can grow far beyond what its original ecosystem would ever allow.
Britain had foxes, stoats and weasels that had coevolved with rabbits for centuries, along with cold winters that shut down breeding for part of the year. Australia offered mild temperatures nearly year-round, soft soil ideal for burrowing, abundant grasses and, critically, no natural predators adapted to hunting rabbits specifically. The European rabbit simply had nothing standing between it and unchecked growth.
The spread itself was staggering by any measure biologists use to track invasions. Rabbits pushed across the continent at a documented pace of roughly 100 kilometers a year in some regions, according to a 2022 study published in PNAS that traced the entire invasion back to Austin’s original release using DNA analysis — startlingly fast for a small ground mammal, reaching Western Australia within decades of that first release near Geelong.
The ecological toll matched the population size. Rabbits stripped native vegetation through overgrazing, accelerated soil erosion and competed directly with sheep and native marsupials for food, contributing to the decline of several native species. The damage was severe enough that Western Australia built the rabbit-proof fence, a barrier stretching more than 2,000 miles, in a largely unsuccessful attempt to halt the westward march.
Australia’s response became a case study in biological control. In the 1950s, authorities deliberately introduced myxomatosis, a virus lethal to European rabbits, and it initially wiped out roughly 90% of the population in affected areas — one of the most dramatic biocontrol successes on record.
But evolution pushed back: surviving rabbits carried genetic resistance, and the virus grew less lethal over successive generations as both host and pathogen adapted to each other, a dynamic confirmed by a 2019 study published in Science — a classic evolutionary arms race in real time. Populations rebounded, prompting the introduction of a second biocontrol agent, rabbit hemorrhagic disease virus, in the 1990s, which is still used to manage numbers today alongside the older virus.
What the rabbit’s takeover of Australia illustrates, more than the headline figure, is a principle invasion biologists return to again and again: population size in a new environment isn’t set by the traits of the species alone, but by everything the environment fails to throw back at it.
A species that looks unremarkable at home can behave like a different organism entirely once the checks are gone. It's also why biosecurity remains such a serious concern for island nations and isolated ecosystems today — the rabbit boom is often cited as the reason Australia now maintains some of the strictest border controls on live plants and animals anywhere in the world, a direct institutional memory of what two dozen animals in a paddock turned into.
The two dozen rabbits Thomas Austin released for a Sunday shoot never left the country. More than 160 years later, their descendants — and the lesson they taught ecologists about invasive species — still have.
Think you understand how evolution shapes a species’ fate like the European rabbit? Test your grasp of natural selection, adaptation and the forces that drive change with this science-backed quiz: Evolution IQ Test