Conservation dollars are and likely always will be limiting. Spending those dollars effectively and efficiently is of pivotal importance (Wilson et al., 2006). Martins et al. (2006) present an analysis of economic costs of invasive mammal eradications on islands that they claim ‘provide conservation planners with a robust, if preliminary, estimate of the cost of any proposed eradication programme.’ Given that invasive mammal eradication is one society’s most powerful conservation tools, this is a badly needed instrument (Donlan et al., 2003). However, while we commend Martins and colleagues’ efforts and goal, the available data are simply and sadly insufficient to provide such a tool. More importantly, providing a naive tool is potentially misleading and dangerous for land managers, conservation practitioners and philanthropists who may turn to the pages of conservation journals for guidance. The costing of eradication campaigns is a complex process. As quantitatively demonstrated by Martins and colleagues, island area plays a major factor in the variation of costs. Using general linear models with a dataset that included 41 eradication campaigns, the authors conclude ‘decision makers considering potential eradication programmes need only know island area, distance from airport (at least in the New Zealand region), and species to be eradicated to make internally consistent and robust first-pass estimates of likely costs.’ In reality, a number of factors and examples strongly suggest that this is not the case. We briefly address five of those issues here. First is the issue of fixed costs. Martins and colleagues claim that due to efficiency gains in the ability to remove invasive mammals from islands, campaigns should be significantly cheaper today than 20 years ago. They go on to state ‘thus, for a hypothetical 10 km island situated 100 km from an airport, costs would decrease from US$ 251 000 if rodents were eradicated in 1983 . . . to only US$ 31 200 if it were done in 2003.’ While the authors are correct in suspecting that the detected effect in their regression model is indeed real, due to certain fixed costs of eradication campaigns, the relationship does not decrease linearly with gains in efficiency. For example, a conservative estimate of the cost of rodenticide bait alone for an aerial eradication campaign on a 10 km island is US$60 000 – twice their predicted total eradication cost (assuming $4 per kg of bait with an application rate of 15 kg ha , cost estimate from Bell Labs, USA). While a few of the rodent eradication campaigns used by Martins et al. reported total costs less than the bait cost estimate at the above application rate, these were conducted on small islands ( 1 km) where either a bait-station approach was used, or perhaps a lower application rate was used but still successful due to the small area of the island. Of the data available worldwide for application rates of past aerial broadcasts, now the most common method used in rodent eradications, the mean application rate is 17.6 kg ha , which is a conservative estimate as more than one bait application is sometimes necessary (range 10–35, n=16; C. J. Donlan, unpubl. data). Secondly, variable costs have a substantial impact on the realized cost of an eradication campaign. While Martins et al. acknowledge that local factors may be important, they fail to appreciate the impact of these factors. Important variable costs of eradication campaigns include (1) needs to mitigate for potential non-target species, (2) the techniques used (e.g. bait stations versus aerial broadcast of bait for rodent eradications), (3) the level of local capacity present, (4) amount of environmental compliance required and (5) the levels of bureaucracy. For example, the cost of campaigns for rodent eradication using aerial broadcast by helicopter depends largely on isolation (e.g. nearest port not airport as remote campaigns are increasingly boat based), while the cost of a campaign using a bait station approach depends largely on labor costs. These variable costs can influence the overall costs of eradication campaigns by an order of magnitude. Black rats Rattus rattus were recently eradicated from Anacapa Island, CA, USA (Howald et al., 2005). Anacapa Island was the first aerial-based
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Feb 16, 2023
Yang Liu + 5
Open Access
