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Cattle (Bos taurus) were liberated on 695 ha Enderby Island, the northernmost of the Auckland Island group, in 1894–96, after a previous liberation had died out. After reaching a peak population of c. 100 animals, they established a relatively stable population of 35–60 animals for the latter half of the 20th century. Eradication was mandated in the 1987 Auckland Islands Management Plan, but proposals for eradication were not universally supported due to the interesting traits of this long-isolated population and its adaptation to the subantarctic environment of the island. Therefore, retrieval of genetic material was permitted before the planned operation. Eradication of the cattle occurred between 1991 and 1993, with at least 47 animals shot in 3 weeks in February 1991, a further two in March–April 1991, and two in December 1991–January 1992. The only two surviving animals were removed alive in February 1993 for captive breeding. The ecological response is considered significant but unable to be completely differentiated from the effects of subsequent eradication of rabbits and mice. Attempts to preserve genetic material via ova, sperm, and live animals met with limited initial success but a small captive population has been established on mainland New Zealand. [ABSTRACT FROM AUTHOR]

Since their liberation in 1807, feral pigs (Sus scrofa) have negatively impacted ecosystem health and processes on subantarctic Auckland Island, New Zealand. Eradication of invasive alien species is often critical to restoration programmes and preventing species extinctions. Eradication programmes utilising multiple techniques have allowed feral pig eradications on large islands. Protracted eradication programmes can have a higher risk of failure due to factors such as biological, logistical, social, and funding support. A temporary local pig eradication pilot study was successfully implemented on a densely vegetated fenced 951 ha peninsula on Auckland Island, emulating the principles set out during the Santa Cruz Island (California, USA) eradication. We applied multiple techniques, each delivered at the appropriate pig population density and within a finite period, to reduce the inherent risk of eradication failure. Aerial hunting was used to reduce the pig population before systematic ground hunting by a team using specially trained dogs removed survivors and validated eradication success. The deployment of a high specification thermal or forward-looking infrared (FLIR) camera in a particular manner greatly improved the efficiency of aerial hunting during this pilot study. The use of passive trapping, Judas pigs and division of the island into smaller fenced units are supplementary methods proposed for the Auckland Island eradication to enhance eradication efficiency as the methods implemented here are scaled up. [ABSTRACT FROM AUTHOR]

House mice (Mus musculus) are an invasive species on Auckland Island in the New Zealand subantarctic and planning for their eradication is underway. Mast seeding events cause rodent populations to irrupt, though little is known about this phenomenon in snow tussock grass (Chionochloa spp.) systems on Southern Ocean islands. The aim of this study was to understand population fluctuations of mouse abundance on Auckland Island for the 2 years following a mast event, and with which tools to monitor abundance, to inform planning of bait application for eradication. Mouse populations were studied using kill and live trapping at two sites on Auckland Island, and mouse density was estimated using spatially explicit capture-recapture models. Mouse population density was highest during summer mast seeding of Chionochloa antarctica and then declined the following winter and subsequently remained low for the following year. Breeding remained seasonal, with a pulse in early summer and a very low level continuing through winter in both years, regardless of mast conditions. These results are similar to those from other cool temperate Southern Ocean islands where seasonal resource availability appears to drive breeding. Throughout the study the capture probability of mice was generally higher when population density was lower, which highlights that conclusions about population trends could be misleading if abundance indices are not calibrated to measures of population density. Mouse eradication should preferentially take place outside of a mast event but would likely still succeed during and following a mast event. Our work fills a key knowledge gap about rodent population trends during mast events for Southern Ocean islands, which is particularly important where eradications are planned. [ABSTRACT FROM AUTHOR]

Primary poisoning is an important method to ensure the successful eradication of cats (Felis catus) from large islands. Poison bait options for feral cat eradications and landscape-scale control in New Zealand are limited at present. As part of the development of a toxic bait for cats that can be aerially distributed, a nontoxic palatability trial was undertaken on Auckland Island to compare three types of prototype meat-based bait and one currently registered fishmeal polymer pellet for their palatability to feral cats and non-target species. Degradation rates of baits over a range of environmental conditions were also estimated by taking photographs of baits at regular intervals and inferring degradation from visual appearance of baits over time. Fourteen individual cats were sighted on 144 occasions with all individuals consuming at least one bait type. Results show that the three prototype meat baits were significantly more palatable than the fishmeal polymer baits. No native non-target animals were observed consuming any of the baits during the trial. Fishmeal polymer baits degraded at a slower rate than the meat-based matrices. Palatability results for the meat-based matrices are encouraging. Further trials of a toxic meat-based bait will be required to assess efficacy in pursuit of a registered product for wider use. [ABSTRACT FROM AUTHOR]

Antipodes Island is part of New Zealand’s World Heritage subantarctic region and hosts special biodiversity values and significant species endemism. Invasive house mice were the only introduced mammal and detrimentally impacted invertebrate and native bird communities. Eradication of mice from Antipodes Island was undertaken in 2016 and confirmed in 2018. We present the monitoring used to confirm eradication of mice and the ecological outcomes measured over the 6 years since the eradication. Result monitoring for confirmation applied a simple regime to search for mice following a delay of two mouse breeding seasons since baiting was completed. Outcome monitoring targeted endemic land bird taxa for possible changes due to operational impacts and ecological recovery following eradication of mice. The operation had no longterm negative impacts and endemic land bird taxa have recovered quickly from variable levels of non-target mortality. Estimates of abundance of Antipodes Island snipe, Antipodes Island pipit and Reischek’s parakeet showed strong long-term positive response to mouse eradication. [ABSTRACT FROM AUTHOR]

A feasibility study for removing feral pigs (Sus scrofa) from Auckland Island trialled feeders monitored by trail cameras to determine their effectiveness for detecting and attracting feral pigs. Ten automatic feeders were installed during January–February 2019 (summer) and again in August–September 2019 (winter) on Auckland Island. They delivered kibbled maize daily for a period ranging from 25 to 37 days. Sites selected for feeder installation needed to be of appropriate relief and area to allow feeder and trap installation, as would occur during an eradication operation. Feeder success varied across sites during the trial. Site selection where there was evidence of fresh pig presence improved the rate of visitation. Feeders offer significant efficiencies to lethal techniques such as trapping by automatically dispensing feed to allow constant supply over a long period. This automation reduces operator effort, but is also advantageous as consistent feed times train pigs to condition their visits so they can be more effectively targeted. In this trial, most visiting pigs returned to the feeder daily from around 15 days after installation. Automated feeders will be an integral component of the proposed methodology for Auckland Island pig eradication to target nocturnal individuals and family groups, and, importantly, reduce the risk of education through non-lethal engagement. [ABSTRACT FROM AUTHOR]

Cattle (Bos taurus) were introduced to 11 268 ha Campbell Island/Motu Ihupuku in 1902 as part of a short-lived farming venture that was abandoned by 1931. The cattle were left to fend for themselves and a small feral population of 10–20 animals persisted for 53 years. The population was largely limited to a small area (c. 440 ha) of the island noted for its limestone geology. Ecological damage was pronounced with churning of the soil, damage to vegetation and probable impact on seabird nesting. Eradication was proposed for 1984 as a precursor to the fencing subdivision of the island for subsequent sheep eradication. Three cattle were shot in January 1984 and although 1–2 animals were known to have survived the cull, for unknown reasons these survivors died out shortly after, and no cattle were seen after winter 1984. Extreme weather events, poor recruitment, and competition with an increasing sheep population may have been partly responsible for the decline to local extinction. The ecological response has been significant but cannot be fully differentiated from the response to subsequent sheep and rat removal. [ABSTRACT FROM AUTHOR]

Feral sheep were eradicated from Campbell Island (Motu Ihupuku) – a National Reserve, Nature Reserve and UNESCO World Heritage Site in subantarctic New Zealand – in three distinct stages from 1970 to 1991. The sheep derived from farming attempts on the island, starting in 1895 and abandoned by 1931. The potential genetic and commercial value of the isolated sheep population meant proposed eradication plans were not wholly supported. Compromise solutions were initially implemented that required the construction of two fences, one in 1970 and one in 1984, to separate three geographic portions of the island. This separation was to facilitate staged removal of sheep and vegetation recovery in one portion of the island whilst retaining the sheep in another portion until eradication was fully committed. Sheep were largely removed by small field teams of experienced hunters using standard ground-hunting procedures in three separate operations, with follow-up operations required to remove small numbers of survivors in all three events. Approximately 7000 sheep were shot over the three operations or associated control/eradication efforts. A significant ecological response has been reported, including a recovery in range, abundance, and individual plant size for subantarctic macroforbs (Anisotome spp., Azorella polaris, and Pleurophyllum spp.), but also for grasses (Chionochloa antarctica and Poa spp.). [ABSTRACT FROM AUTHOR]

Auckland Island, the fifth largest island in New Zealand, is the only island in New Zealand’s subantarctic region where introduced mammalian pests remain (pigs, Sus scrofa; mice, Mus musculus; cats, Felis catus). The island has unique biodiversity and is a key site for progressing New Zealand’s goal to be free of several introduced predators by 2050. Recent island eradication successes have rekindled interest in eradicating pests from Auckland Island, and for the first time considering all three pests in one project. Over a 3-year period, we tested the feasibility of eradicating pigs, mice and cats by looking at what it would take to succeed, rather than what we could practically deliver with the tools we currently have. We proposed adaptations to current methods and used an evidence-based approach by undertaking large-scale field trials to test uncertainties and emerging technologies in-situ. We gathered data and evaluated proposed methods against five established principles of eradication while considering the logistics and infrastructure requirements of the project. Eradicating pigs, mice and cats from Auckland Island is worthwhile and feasible but dependent on further development of emerging technologies and capabilities for efficient delivery with an acceptable level of risk. Three eradication operations are required with specific sequencing and timing, supported by initial establishment of infrastructure. The project needs a large investment spread over 8 to 10 years to yield permanent and internationally important benefits with low ongoing cost to sustain. The feasibility study exposed the project’s scale and was used to inform decision makers, who postponed the work in 2020 in response to the economic impacts of COVID-19. The study focusses future preparations on identified planning issues and dependencies to progress project readiness in anticipation of it being launched when economic conditions allow. [ABSTRACT FROM AUTHOR]

As a major threat to New Zealand’s biodiversity, feral cats (Felis catus) are the subject of planned eradications on a number of offshore islands, including Rakiura Stewart Island. We used camera traps to estimate population density of feral cats on the north-east coast of Rakiura, and to investigate their movement behaviour and detection probability. We also used camera footage to compare the consumption of two types of non-toxic sausage baits (chicken and rabbit) with a view to future use of toxic baits. Population density of feral cats was likely between 1 and 2 cats per km². Non-target species (rats and possums) removed more than half the baits, greatly reducing bait availability for feral cats. Deer and birds (including kiwi) encountered baits but did not eat them. Cats had an apparent preference for chicken over rabbit baits, although small sample sizes prevent firm conclusions. Both bait types appeared to decline rapidly in palatability, and no baits were consumed by cats more than 5 days after deployment. Future trials and baiting regimes should consider ways to improve bait availability. Increased bait density, exclusion of rats and possums and/or more frequent replacement of baits will likely increase encounter rates by feral cats. [ABSTRACT FROM AUTHOR]

Restoration initiatives of ecosystems transformed by human actions require optimisation of eradication measures of introduced species, particularly in fragile insular ecosystems. We studied aspects of the spatial ecology of introduced feral cats (Felis catus) on subantarctic Auckland Island of New Zealand to assist eradication efforts of pests from this remote, biologically rich island. Firstly, we estimated home range sizes and identified core areas of activity based on movement-rooted dynamic Brownian bridge models. Second, we used resource selection functions with generalised linear mixed models to identify seasonal patterns of space use associated to topographic, vegetation and other landscape predictors. Lastly, we quantified cats daily movement rates within home ranges. Average home range size was larger than on other offshore islands and mainland New Zealand, which might relate to lower cat densities and the abundance and predictability of food resources on the island. Cats mostly selected mosaic areas of forest, shrubs and tall tussocks near the coast, and in predominantly flat areas or nearby steep cliffs, which are all typical habitats of seabirds and terrestrial birds. Cats also selected alpine short tussocks during the cold season, likely related to the upsurge of mice (Mus musculus) due to tussock mast seeding and to transiting to steep cliffy areas. Male cats had home ranges that were larger, contained more core areas, and covered longer daily distances in the warm season than females, which might be associated with different breeding and reproductive behaviour. Eradication tools will need to target all habitats on Auckland Island with increased efforts in areas of identified higher use by cats. Understanding aspects of pest species’ spatial ecology on offshore islands worldwide can assist decision-makers in optimising eradication programs such as Predator Free 2050 in New Zealand. [ABSTRACT FROM AUTHOR]