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Poison operations are a widely used technique for rodent control in the indigenous forests of New Zealand. This study examined the bait-take and rat monitoring data obtained for continuous poison operations at Boundary Stream Mainland Island (BSMI), Hawke’s Bay, between 1996 and 2007. Since the beginning of the Mainland Island project at BSMI in 1996, 800 ha of indigenous forest have been treated with an ‘Integrated Pest Management’ approach, in which rodents (primarily ship rats) have been targeted by consecutive ground poison operations. The aim of the intensive pest control was to allow the ecosystem to recover and provide a safe environment for threatened native bird species to recover or be re-introduced. Another important aim of this pest control is to provide experience and expert knowledge in management techniques especially applicable to the protection of indigenous habitat on the New Zealand mainland. This research study had two main aims: to identify spatial patterns of the rodent population at BSMI and to determine the efficacy of the different rodenticides applied for their control. The distribution of the rodent population was investigated by spatial analysis of bait-take across the reserve and through time. Visualisation of high and low bait-take areas revealed that there was a noticeable reinvasion from adjacent unmanaged native forests, but not markedly from exotic forest or pasture. Reinvasion from small and isolated adjacent forests ceased to be noticeable consistently after approximately four years of the poison operation, while a large scenic native reserve, as well as a narrow part of the treatment area surrounded by many native bush patches, were continuously affected by reinvasion through the entire project time. Bait-take was visibly higher after the bait had either been removed, or left in the field unserviced, over winter. No consistent areas of no bait-take were identified. Further statistical analysis of bait-take data revealed that bait-take was higher in bait stations within 150 m of the treatment edge than interior bait stations. Bait-take in broadleaf/tawa/podocarp forest was significantly higher than in kamahi/kanuka/rewarewa, beech and cloud-cap forest. The second aim of the study was to determine the efficacy of the various bait types with different active ingredients used during the operation. Rat monitoring data, namely rat tracking indices (RTI) obtained from tracking tunnels, were statistically modelled using Generalised Linear Models. Diphacinone cereal pellets (Pestoff® 50D, 0.05g/kg diphacinone) obtained the lowest RTI, followed by pindone cereal pellets (Pindone Pellets®, 0.5g/kg pindone), brodifacoum cereal pellets (Pestoff® 20p and Talon®, 0.02 g/kg brodifacoum), coumatetralyl paste (Racumin®, 0.375 g/kg) and diphacinone bait blocks (Ditrac®, 0.05 g/kg). Cereal pellet baits worked better than any other bait type used at this location. Season had no statistically significant effect on either RTI or bait-take estimates. The overall goal of the poison operation to decrease rat numbers, and to maintain low levels, has been met. However, the results of this study suggest that baiting needs to be done continuously and over the entire treatment area. Edge bait stations – particularly next to adjacent native forests – should be prioritised to target reinvading rodents. Poisons presented in cereal pellet baits should be preferred to other bait types. Both pindone and brodifacoum showed very good results, as well as diphacinone in cereal pellet baits.

Brodifacoum is a highly effective anticoagulant rodenticide that presents a secondary hazard to some non-target wildlife. The high acute toxicity of brodifacoum to mammals and birds, and its prolonged persistence in liver predicates secondary risk to predators and scavengers of poisoned rodents. Hence there is a need to improve ability to monitor and predict hazards of brodifacoum to non-targets, and optimise use patterns accordingly. Use of a less persistent anticoagulant rodenticide, diphacinone, is an alternative approach currently under investigation in New Zealand. This thesis describes a series of laboratory and pen studies that address information gaps relevant to the assessment of non-target hazards in continued use of brodifacoum, and of using diphacinone as an alternative. Non-lethal techniques for determining sublethal brodifacoum exposure in birds was investigated in chickens. Elevation of prothrombin time was a less reliable index than residual concentrations in tissues. Samples requiring less invasive procedures, such as dried blood spots or faeces, have potential to detect recent sublethal brodifacoum exposure and refinement of these indices could be useful in proactive monitoring of avian wildlife. Residual brodifacoum in eggs of sublethally-exposed hens raised further questions regarding wider non-target hazard and adverse effects on development of fertile eggs or chicks. A laboratory trial with rats found a positive correlation between residual brodifacoum concentrations in liver and the amount of brodifacoum ingested as bait. An estimated 14-22% of ingested brodifacoum was excreted in rat faeces in the period between ingestion of a lethal dose and death, indicating another potentially significant environmental pathway for brodifacoum transfer. In considering diphacinone as a less persistent alternative rodenticide to brodifacoum, evaluation of residual concentrations and persistence in pig tissues was required to estimate secondary hazard to human consumers and adequate with-holding periods for hunting feral pigs in areas where diphacinone was applied. A pen trial showed that domestic pigs were more susceptible to diphacinone toxicity, and thus primary poisoning risk, than previously estimated. Hepatic half-life of diphacinone in pigs was approximately 14 days, indicating reduced persistence in comparison to brodifacoum and enabling estimates of with-holding periods for hunting feral pigs from areas where diphacinone baits were applied. To investigate potential hazards of diphacinone use to invertebrates a trial using tree weta, a native New Zealand invertebrate, was undertaken. Weta readily ate diphacinone wax block baits with no mortality or weight loss evident, indicating low susceptibility. Residual whole-body diphacinone concentrations did not increase with the amount of diphacinone bait eaten. A simple, deterministic risk assessment suggested that, as a single secondary exposure, the maximum diphacinone concentration measured in weta would present a low risk to non-target birds. Given international recognition of the high secondary hazard and corresponding restrictions on use of brodifacoum, continued availability of brodifacoum to non-licensed users and sustained field applications for possum and rodent control in New Zealand is an exceptional use pattern. New data in this thesis suggest that baiting strategies that minimise the amount of brodifacoum available in the environment are important and regulatory review of some New Zealand brodifacoum applications should address this. In parallel, development of diphacinone as an alternative to brodifacoum should continue, as new data here confirms lower persistence in mammalian liver than brodifacoum, and also indicates low toxicity to invertebrates. However further investigation of multiple-exposure hazard and potential sublethal effects of diphacinone on non-target mammals and birds is warranted before extensive and sustained field applications of diphacinone are undertaken.