The European rabbit (Oryctolagus cuniculus) is a damaging invasive mammal species, particularly in regions like Australia and New Zealand where it was introduced. Its grazing habits cause significant land degradation and erosion, and rabbits compete directly with livestock and native fauna for forage. The economic impact on agriculture alone is estimated to be hundreds of millions of dollars annually. Successfully managing these populations requires a sustained, multi-faceted approach, as complete eradication is extremely difficult.
Biological Factors Hindering Control
A challenge in controlling the European rabbit population stems from its remarkable reproductive capacity. Females (does) reach sexual maturity as early as four months and can produce five or more litters annually. The gestation period is short (about 30 days), and a doe can mate again almost immediately after giving birth, allowing populations to multiply rapidly.
The rabbit’s complex burrow system, known as a warren, further complicates control efforts. Warrens provide protection from predators, extreme weather, and surface-based control methods. These underground networks can extend up to 3 meters deep and 45 meters long, offering secure shelter. This protected habitat must be directly addressed to achieve lasting population reduction.
Physical and Chemical Removal Methods
Direct intervention through physical and chemical methods provides immediate, localized population knockdown. Chemical control often involves applying poison baits, typically sodium fluoroacetate (1080) or Pindone. The single-feed poison 1080 requires a strict pre-feeding period (8 to 10 days with non-toxic bait) to ensure maximum uptake. Pindone, a chronic anticoagulant, requires multiple feedings over several days, often using a pulse-baiting technique after non-toxic pre-feeding.
Physical control methods focus on destroying habitat and excluding rabbits from sensitive areas. Warren destruction, or ripping, uses heavy machinery to collapse tunnels to a depth of 700 to 900 millimeters, rendering the structure unusable. This is typically done by cross-ripping to guarantee all burrows are destroyed. If warrens cannot be ripped due to obstructions, fumigation with agents like aluminum phosphide, which releases toxic phosphine gas, eliminates rabbits underground.
Exclusion fencing is a long-term method for protecting high-value land, requiring specific construction standards:
- The wire netting must have a small mesh size (40 millimeters or less).
- The fence must stand at least 90 centimeters high to prevent jumping.
- The netting must be buried at least 15 to 20 centimeters deep, often with the bottom edge turned outward in an ‘L’ shape, to prevent burrowing.
Shooting and trapping are supplementary measures used to target surviving rabbits in low-density populations or during follow-up operations.
Viral Biocontrol Strategies
The most impactful population reductions have been achieved through viral biocontrol agents. Myxomatosis, caused by the Myxoma virus, was released in the 1950s and initially caused mortality rates exceeding 90 percent. However, the virus naturally attenuated over time, becoming less lethal, while rabbits developed genetic resistance. This reduced the virus’s long-term effectiveness as a sole control measure.
The introduction of Rabbit Hemorrhagic Disease Virus (RHDV), a calicivirus, provided a second major wave of suppression starting in the mid-1990s. RHDV causes a highly fatal disease; its initial strain, RHDV1, was effective in arid regions. The emergence of the RHDV2 variant in the 2010s complicated control, as this strain can lethally infect young rabbits previously resistant to RHDV1. RHDV2 rapidly became the dominant circulating strain and remains the most effective large-scale population suppressor available.
Viral biocontrol is a self-disseminating tool that continuously suppresses population numbers, though it does not achieve complete eradication. The viruses rapidly reduce population density, creating a window for land managers to apply conventional control methods. These biological agents must be integrated with other management techniques to manage the inevitable population recovery that occurs as resistance increases.
Implementing an Integrated Management Strategy
Effective, sustained rabbit control relies on an Integrated Pest Management (IPM) strategy, combining multiple control methods in a coordinated sequence. The process begins with a large-scale population knockdown phase, best accomplished using self-disseminating biocontrol agents or chemical baiting programs like 1080.
Following this initial reduction, the strategy moves into a “knockout” phase focused on eliminating survivors and reducing breeding capacity. This stage involves physical methods, primarily the destruction of warrens through deep ripping, and the installation of exclusion fencing. Removing the warren eliminates the secure breeding habitat and is the most important physical action for preventing population rebound.
The final “mop-up” phase involves continuous monitoring and the targeted use of supplementary controls. These include fumigation of warrens that could not be ripped, or shooting to remove remnant pockets of rabbits. This sequential application of methods, where suppression is followed by habitat destruction, is the only practical way to minimize the damage caused by the European rabbit population.