Optimising bait-station delivery of population-control agents to brushtail possums: field test of spatial model predictions
Adrian Monks A B and Daniel M. Tompkins AA Landcare Research, Private Bag 1930, Dunedin 9054, New Zealand.
B Corresponding author. Email: monksa@landcareresearch.co.nz
Wildlife Research 39(1) 62-69 https://doi.org/10.1071/WR11066
Submitted: 5 April 2011 Accepted: 6 November 2011 Published: 27 February 2012
Abstract
Context: Low-volume control agents based on new biotechnologies are likely to be point-delivered to wildlife populations using devices such as bait stations. However, data and theory to underpin the development of strategies for such a use of bait stations are lacking.
Aims: In a large-scale replicated field trial of brushtail possum (Trichosurus vulpecula) populations, we estimated the levels of coverage achieved with bait-station grids at three densities (0.2, 0.6 and 1.0 ha–1), with and without pre-feeding, to test the predictions of an existing model of bait-station delivery based on relationships derived from leghold trapping.
Methods: We first marked possums using conventional capture–mark–recapture techniques, and then estimated population coverage by recovering animals poisoned by encapsulated cyanide delivered by the bait stations.
Key results: The two key model predictions, that 90% population coverage could be achieved at 0.6 bait stations per hectare and that pre-feeding was not required to achieve this level, were not upheld by the field trials. Instead, there was a poor fit between model predictions and observed levels of population coverage. An investigation of key model assumptions demonstrated issues with both model structure and parameterisation.
Conclusions: Neither previously documented relationships for possum interactions with leghold traps, nor correlations between possum interaction rates with such devices and bait stations, are generically applicable across all populations.
Implications: While the existing model of bait-station delivery to possums fits the data for some field operations and trials, it is not applicable to all populations. Incorporating habitat and seasonal effects on possum home-range behaviour could potentially improve model prediction. Our results also have implications for the accuracy of index-based methods of possum population monitoring that use leghold traps, such as the Residual Trap Catch Index.
Additional keywords: bovine tuberculosis, fertility vaccine, leghold trapping, marsupial, population monitoring, RTCI, wildlife management.
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