Performance and humaneness of chloropicrin, phosphine and carbon monoxide as rabbit-warren fumigants
F. Gigliotti A , C. A. Marks B C and F. Busana AA Vertebrate Pest Research Unit, Department of Primary Industries Research Victoria, PO Box 48, Frankston, Vic. 3199, Australia.
B Nocturnal Wildlife Research Pty Ltd, PO Box 2126, Wattletree Road Post Office, East Malvern, Vic. 3145, Australia.
C Corresponding author. Email: camarks@attglobal.net
Wildlife Research 36(4) 333-341 https://doi.org/10.1071/WR06020
Submitted: 24 February 2006 Accepted: 12 March 2009 Published: 1 June 2009
Abstract
Concerns about the humaneness and efficacy of chloropicrin (CLPN) and phosphine (PH3) as warren fumigants for the control of European rabbits (Oryctolagus cuniculus) prompted this investigation into the field performance and humaneness of carbon monoxide (CO) as an alternative fumigant. Comparative trials were performed in a naturally formed 1.3-m3 warren fitted with gas, temperature and humidity sensors as well as infrared cameras and microphones. Trials used concentrations of 5% and 6% CO introduced at 400 L min−1, and standard field practices for CLPN and PH3. Rabbits exposed to CLPN displayed signs of intense irritation and extreme distress during a lethal toxicosis lasting a mean of 82.5 min, supporting previous conclusions that CLPN causes suffering. Phosphine gas killed 10 of 12 rabbits, in a mean of 225.3 min. This relatively poor performance was attributed to the low rate of gas production and passive diffusion through the warren, reflected in highly variable warren concentrations between trials. Phosphine caused greater agitation on the onset of first symptoms than did CO; however, the behavioural symptoms after collapse were broadly similar. Carbon monoxide dispersed evenly in the warren, caused no immediate irritation or distress and produced a gradual stupor before unconsciousness and death. Concentrations of 6% CO killed rabbits almost three times faster than 5% CO, suggesting that relatively small increments of concentration and exposure time are crucial in obtaining a consistently rapid death. A concentration of 6% CO caused death in 8 of 10 rabbits in a mean of 28.3 min; some 2.9 and 8 times faster than CLPN and PH3 respectively. The time from collapse until death did not appear to be appreciably different for PH3 and 6% CO. The present study demonstrated that CO has potential as a rapid-acting, humane and effective fumigant for rabbit control.
Acknowledgements
Special thanks go to the many contributors who freely gave their time and experience, including Dr Marc Marshall (Monash University), Peter Weare (hypobaric engineer), Darren Todd (Bosch Australia), Wim Vanden Hil (Allara), Tim Passmore (Air Liquide), Tony Ciaglia (Autlec), Jim Blight (AMCOSH), Frank Seabridge and Paul Hay. This study was funded by the Catchment and Water Division of the Department of Sustainability and Environment (Victoria). All research procedures were carried out in accordance with the Australian Code of Practice for the Care and Use of Animals for Scientific Purposes and were approved by the Primary Industries Research Victoria Metropolitan Animal Ethics Committee (AEC) as Protocol 2126. The use of CO in trials was in accordance with National Registration Authority (NRA) Permit No. TPM0015A. Many thanks go to Dr Kate Blaszak and the late Dr John Barnett for reading an earlier draft of this paper and providing constructive feedback. The paper benefited from comments received from three anonymous referees and helpful advice from Dr Andrea Taylor and other editorial staff at Wildlife Research.
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