Review of the reporting of ecological effects of rodent eradications on Australian and New Zealand islands

Abstract

Island species are susceptible to invasive mammals because of their small populations, specialised habitats and reduced likelihood of recolonisation. For more than 50 years, invasive mammals have been eradicated from islands around the world. Despite the success of eradications, there are few publications in the primary literature detailing the ecological benefits and consequences of these eradications. Here we conduct a review of the published literature focussing on rodent eradications conducted on Australian and New Zealand islands and we evaluate the extent of reporting of non-target mortality and ecological monitoring following an eradication. A search of the Database of Island Invasive Species Eradications website identified that successful, whole-island rodent eradications were conducted on 66 Australian and 124 New Zealand islands in the period from 1964 to 2016. We found that non-target mortality was rarely ever reported (3% and 12% for eradications on Australian islands and New Zealand islands, respectively). Results of any quantitative ecological monitoring following eradications were published for only 10% of all successful rodent eradications on Australian islands and 19% of all eradications on New Zealand islands. There also has been no change in reporting of potential benefits and consequences of rodent eradications in Australia and New Zealand over the last few decades despite an increased awareness of the problem of under-reporting. We discuss the detailed benefits and consequences of these eradications in Australia and New Zealand and highlight the need to incorporate ecological monitoring into new projects to document benefits and consequences of eradications to inform future eradications.

Nesting Success and Nesting Height in the Critically Endangered Medium Tree Finch (Camarhynchus pauper)

“…Planning for non-target mortality is a cornerstone risk management component of eradication projects [82], and the mitigation plan includes a safeguard population (i.e., a small genetically representative number from different island zones) for all Darwin's Finch species and also Short-eared Owls held in captivity until traces of poison have disappeared from the environment [83,84]. Invasive rats have been eradicated from 447 islands [2,85] and, in general, the local flora and fauna have shown a rapid recovery response [81,[86][87][88][89][90][91][92]. A planned rodent eradication from Floreana Island is expected to improve nesting success in Medium Tree Finch, though monitoring is required to measure the impact of Short-eared Owl, Smooth-billed Ani and vampire fly.…”

The global contribution of invasive vertebrate eradication as a key island restoration tool

“…The true number of invasive species eradication events on islands will be greater than the number reported here for multiple reasons. First, publication of invasive species eradication attempts on islands remains relatively uncommon 51 with results reported in this study often found in unpublished reports. Second, authors of this paper are first-language English speakers and while Google Translate was used to translate non-English reports, events may be overlooked due to this language bias 52 .…”

Effects of an island-wide rodent eradication programme on two threatened bird species

“…This study is one of few that assessed quantitatively the ecological effects of an island-wide rodent eradication on native birds, including one terrestrial bird species, using pre-and post-eradication data (Jones et al 2016;Segal et al 2021a). As well as informing stakeholders and demonstrating a return on investment for funding bodies, measuring the ecological benefits and consequences of rodent eradications may contribute to the planning and management of future eradications.…”

“…However, only 22 studies of 63 species documented specific responses to eradications such as trends in abundance or reproductive success and few of these contained quantitative information (Jones et al 2016). Reporting of the ecological benefits of island-wide rodent eradications is also lacking in Australia, where ecological monitoring was undertaken for less than 20% of all rodent eradications (Segal et al 2021a). Moreover, the failure to collect pre-eradication data prevents any quantitative comparison with post-eradication data (Buxton et al 2016;Croll et al 2016), limiting the ability to assess the ecological benefits and consequences of eradication programmes.…”