New Zealand Journal of Zoology abstracts

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Enhancing maintenance control of possum populations using long-life baits

David R. Morgan

Landcare Research
P.O. Box 69
Lincoln 8152
New Zealand
email: morgand@landcareresearch.co.nz

Abstract  Possum populations must be maintained at very low density if the aims of Tb eradication and conservation of particularly vulnerable native species are to be met. The present tactic of initial “knockdown” followed by annual maintenance control allows for reinfestation in between annual operations. Development of toxic baiting methods for “continuous” control of possum populations is therefore desirable. Six bait-type/presentation-methods designed for prolonged field life were exposed to field conditions at a forest edge site in Westland. Samples of baits were collected at 2-monthly intervals for up to 26 months, and assessed for palatability to possums and toxicant concentration. Regression analysis was used to predict the time at which reductions in palatability and toxicity would make the bait ineffective. Field life varied between 2 and >26 months. The most durable option tested was a solid gel bait containing cholecalciferol and presented in a purpose-designed bait station. This option was selected for assessment in continuous control of possums in forest-edge habitat in Westland. Baits were placed up trees beyond the reach of livestock and left in place for 10 months. Trap-catch monitoring showed these baits did reduce the number of possums, but only after improving the visibility, attractiveness, and accessibility of bait stations. As the study predicted that cholecalciferol gel bait should remain effective for >2 years in the field, there appears to be considerable potential for improving the efficiency (and probably environmental safety) of long-term control using this new tool.

Keywords  possum; Trichosurus vulpecula; pest control; baits; bait palatability; 1080; cholecalciferol; brodifacoum; cyanide

Z03042; Received 10 December 2003; accepted 12 July 2004; Online publication date 24 November 2004

New Zealand Journal of Zoology, 2004, Vol. 31: 271–282
0301–4223/04/3104–0271 © The Royal Society of New Zealand 2004

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