Invasive ship rats (Rattus rattus) are a major threat to the native species and ecosystems of islands. We used 10 self-resetting traps (A24 rat and stoat traps, Goodnature Ltd., Wellington, NZ), along with existing single kill DOC200 traps at two devices per hectare on a 9.3 hectare island in New Zealand to reduce rat numbers and ideally achieve eradication. Each self-resetting trap was monitored with motion-activated cameras to analyse rat behaviour and A24 kill numbers were documented using Goodnature digital strike counters. The traps were checked on 10 occasions from August 2016 to October 2017. The videos documented initial high rat activity on the island, which reduced over time following initial trapping success. An immediately obvious neophobic response towards the A24 traps was not observed. Rats interacted with the A24 traps within hours after initial deployment and 60% of the traps were triggered in the first night. After three nights, all traps were triggered at least once. While rats interacted with the traps at all times of the year the number of observed trap-triggers was relatively low. High number of interactions resulted in high kill numbers in late spring when population size was increasing and seasonal food abundance had not yet reached its peak. A second peak was observed in late autumn when rat abundance was presumably high. Recruitment of naïve individuals was a probable cause for high kill numbers during the breeding season. In winter, when rat abundance was presumably low, a few individuals were the likely cause for a high number of interactions while kill numbers were low. A knock-down (i.e. suppression from high to low abundance) of rats using both trap types was achieved in the first 100 days. However, kill numbers of A24s declined over time. After the initial suppression, the number of rats killed was insufficient to offset intrinsic population growth and reinvasion from the adjacent coast, thereby preventing eradication.

Lethal trapping of island invasive rodents is a critical practice used by management organizations to protect native biota. Carcass detection from lethal trapping is dependent on the trapping method, carcass palatability, and scavengers present. Goodnature A24 self-resetting rat traps are an effective tool in remote areas and complex terrain because traps can be visited at 4–6 month intervals and produce multiple carcasses during that interval. The goal of this study was to determine whether we are a) underestimating target mortality with carcass counts and b) failing to detect non-target mortality between A24 trap checks at two field sites on the island of Kauai. Both sites have established Goodnature A24 trap grids with 300 A24s deployed by the Kauai Forest Bird Recovery Project (KFBRP), and one site is fenced to exclude invasive ungulates. KFBRP conducts routine trap checks every four months, finding 0–3 rat or mouse carcasses at each trap. We assumed that traps kill more animals than indicated by carcass counts because 75% of traps have counters to record when traps fire, and counter tallies usually exceed carcass counts. In 2018 and 2019, several bird carcasses were found under traps; therefore, we needed to investigate the likelihood that non-target mortality went undetected. In May 2019, we placed 60 carcasses (30 non-native birds and 30 rats) at a fenced site, and 60 carcasses (30 bird, 30 rat) at an unfenced site, in both gulches and uplands. Carcasses were periodically surveyed for 120 days after deployment. The unfenced site had greater removal rates, notably in gulches; 33 of 60 carcasses remained detectable, compared to 52 of 60 carcasses at the fenced site. Bird and rat carcasses did not differ in persistence, and taxon did not affect scavenger preference. These results suggest that significant non-target mortality has not gone undetected in our A24 trap grid because we are likely to detect most target and non-target carcasses after four months in fenced areas, and especially upland unfenced areas. However, we are less likely to detect carcasses in the unfenced gulches where ungulate scavengers are prevalent, and increased monitoring may be needed in such gulches.

House mice (Mus musculus) are worldwide pests in urban, agricultural, and natural settings. Goodnature® A24 rat+stoat self-resetting traps (A24s) are used globally for invasive rat control, yet adequate efficacy testing has not occurred against house mice. Our objective was to test efficacy of A24s against wild house mice. We first used cage/pen trials to determine whether the time from A24 impact to death was short and met international animal welfare standards (New Zealand National Animal Welfare Advisory Committee [NAWAC]). We also varied lure type (peanut butter vs. Goodnature chocolate lure) and trap configuration (vertical vs. angled in a trap stand) to assess trap attractiveness. Of the 80 mice tested, 67 triggered A24s, and just three required our intervention and euthanasia because they were still alive 2 minutes after being struck by the A24. Time to death for the remaining 64 mice averaged (± SE) 50.9 ± 2.6 seconds (median: 46.8 seconds, range: 19.8–120 seconds). Thus, A24s passed NAWAC standards of Class B for kill-traps against house mice. Although mice frequently contacted A24s during the 3-day trials, average time to trigger was 4.6 ± 0.6 hours and 13 mice never triggered A24s. Baiting A24s with peanut butter resulted in significantly greater mortality (98%) than by using Goodnature chocolate lure (70%). Mice triggered A24s baited with peanut butter 2.3 times faster than Goodnature chocolate lure, and 2.7 times faster if A24s were angled in trap stands rather than positioned vertically. In further trials, we released groups of up to five mice into a 24 m² arena containing either two A24s or two snap-traps+two A24s. Two A24s in the arena resulted in all 25 mice triggering A24s and dying; mice were undeterred from triggering A24s when mouse carcasses were near A24s. When snap-traps and A24s were present, one of 38 mice survived the 9-day trials. If snap-traps were reset each 24 hours they killed significantly more mice than A24s, yet if they were not reset during trials the A24s killed significantly more mice than snap-traps. A24s appear adequate for use against house mice, especially if baited with peanut butter and angled in trap stands.

Invasive black rats (Rattus rattus) are one of the most damaging vertebrate species to agriculture globally. In citrus orchards, rat damage includes fruit consumption and contamination, girdling of branches, and gnawing irrigation equipment. Managing black rats in citrus is challenging given the abundance of food and cover provided by the trees year-round. Anticoagulant rodenticide applications, such as diphacinone-laced baits applied via bait stations, are sometimes used to manage black rats in orchards, but have not been tested in an evergreen crop like citrus. Goodnature A24 self-resetting rat traps are increasingly used to manage black rats for conservation purposes, but have not been tested in agricultural settings. Therefore, we used a replicated treatment-control randomized block design to test the efficacy of: 1) 0.005% diphacinone-treated oats applied via elevated bait stations and 2) A24 traps that were elevated to approximately 1 m height to match the bait station heights. This study was conducted across four citrus orchards in the southern San Joaquin Valley, California, to better identify how to implement these tools to manage invasive black rats in this economically important crop. Although neither trapping nor rodenticide baiting yielded the desired reduction in black rats across all sites, we identified strategies that hold promise for future testing. For rodenticides, reducing the spacing between bait stations may increase efficacy by increasing encounter rates by rats. For trapping, the use of a platform under the A24 traps appeared to increase its effectiveness by allowing easier access to the trap trigger. Furthermore, reducing spacing between traps may also yield better results. Ultimately, a management plan that combines trapping and rodenticide baiting may prove more efficacious than our initial study design and should be investigated further.