Abstract
New Zealand is a globally unique oceanic island due to the high prevalence of alpine ecosystems and a biota that evolved in the absence of mammals. Introduced mammalian predators are the leading cause of extinctions in New Zealand and have been implicated in the declines in abundance of many alpine species. However, landscape scale techniques to monitor the relative abundance and control of pest species in alpine areas have not been developed. The aim of this study is to address these shortfalls by modifying footprint tracking tunnel methods, trialling different aerially-applied 1080 pest control regimes, and by intensively monitoring a predator-sensitive alpine passerine to determine if these methods have conservation outcomes.
Footprint-tracking tunnels are a cost-effective and widely used method to measure the changes in the relative abundance of mammals. In New Zealand, indices derived from footprint tracking tunnels are used to assess the efficacy of pest control operations using aerially-applied 1080 poison. The efficacy of landscape scale predator control using 1080 in alpine areas is unknown and the current footprint-tracking methodology appears unreliable at detecting pest species with a low probability of detection, particularly in alpine areas. This study used a model selection approach to investigate if increasing the survey interval and spatial distribution of footprint-tracking tunnels increased the sensitivity of the indices for mustelids (Mustela spp.), rats (Rattus spp.) and mice (Mus musculus). I then investigated if aerially-applied 1080 poison effectively controlled each predator in alpine areas. I found that 21-night surveys were more sensitive than the established best practise for mustelids in forested and alpine areas and for rats and mice in alpine areas. Aerially-applied 1080 poison effectively reduced mustelid abundance in forested and alpine areas, and mice were unaffected. Rats were the most uncommon introduced predator in alpine areas, but appeared to benefit from a meso-predator release when alpine areas were excluded from 1080 operations.
The reproductive success, survival and population trends of the endangered alpine rock wren (Xenicus gilviventris) was intensively monitored in areas with and without 1080 predator control. I then used a model selection approach to test which explanatory variables best explained my data. Fixed trail cameras on nests demonstrated that mustelids, rats and snowstorms cause significant adult mortality and nest failures. Landscape scale aerially-applied 1080 poison effectively reduces alpine predator abundance and results in substantial increases in nesting, survival and territory occupation estimates for rock wren which results in population increases where rock wren occur. These effects last for at least 2 years. I could not rule out potential by-kill of rock wren resulting from 1080 sown in alpine areas, because mortality occurred unevenly at the one site when a 1080 operation and a snowstorm occurred in succession. However, this risk is low, as rock wren have demonstrated no susceptibility to 1080 poisoning at another site and have suffered nest failures and mortality in snowstorms at both sites, in years where 1080 has not being implicated. However, 1080 applied only to treeline resulted in equally effective mustelid suppression, thus removing the by-kill risk to rock wren, but increased the risk of rat predation. Mice were unaffected by either 1080 sowing strategy used in this study.
Tracking indices for mustelids best explained changes in rock wren nest predation rates. Reliable monitoring of mustelids, rats and mice in alpine areas, or in areas where these predators are uncommon, can now be undertaken. Management with aerially-applied 1080 is an effective landscape scale tool for alpine pest control, therefore a management tool now exists to reverse the decline of mustelid and rat sensitive alpine species on a landscape scale. Endangered rock wren populations will benefit greatly from an increased use of 1080.
Further research is required to resolve the uncertainty around the risk of 1080 in alpine areas to rock wren, as well as how mustelids, rats and mice can be controlled in more expansive alpine areas.