The animal welfare impacts of a gas explosive device used for the management of wild rabbits in Australia

Context Destruction of rabbit warrens to prevent re-invasion is an important component of integrated rabbit management. Ripping, and less commonly blasting with explosives, are used to destroy warren systems and to kill any rabbits remaining in warrens, usually after the population has already been reduced. However, the use of these methods can sometimes be constrained by vegetation, topography, presence of culturally significant sites or important habitats, or they may be inefficient or expensive due to the low density of warrens. Gas explosive devices provide an alternative method in these situations; however, little is known about their animal welfare impacts. The R3 Unit is a gas explosive device used in Australia. It pumps a calibrated mixture of propane and oxygen into a warren and then ignites the mixture, causing a blast wave to travel through the warren. Aims To determine the animal welfare impacts of the R3 Unit gas explosive device and to assess its effectiveness at achieving a rapid death in wild rabbits. Methods Trials of the R3 Unit were initially conducted in artificial warrens to determine the relationship between blast pressure, warren size and structure. We then assessed the extent of injury and probability of death of rabbits in both artificial and natural warrens. Key results As blast pressure increases within a warren, probability of death also increases. Blast pressures exceeding 56 psi will render rabbits unconscious, but a blast pressure of at least 67 psi is required to kill rabbits quickly and humanely. Sublethal blasts at lower pressures result in significant injuries that lead to severe suffering. Conclusions The R3 Unit can humanely kill rabbits when the blast pressure is sufficient to cause immediate unconsciousness and death (without regaining consciousness). To achieve adequate blast pressure, warrens must be small, with a diameter no more than 4 m, and all entrances must be sealed. Implications The R3 Unit can provide an effective alternative to warren ripping and blasting in certain situations. However, to ensure the device is used correctly to minimise animal welfare impacts, operators must be trained in its use and follow best practice procedures.