Browsing by Author "Armstrong DP"

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    Apparent resistance to brodifacoum in Rattus rattus in a New Zealand site with no history of anticoagulant-based rodent control
    (CSIRO Publishing, 2022-07-07) Sran SPK; Gartrell BG; Fisher P; Armstrong DP; Belmain S
    Context: Anticoagulants have been used in New Zealand for decades, but few data are available on the sustainability of these toxins for rodent control. It is important to regularly monitor for resistance in long-term brodifacoum-use areas and establish a database for future references. Aims: This study aimed to estimate the effective dose (ED50) of brodifacoum for ship rats from an area of New Zealand with no history of brodifacoum use, in order to establish a blood-clotting response test for assessing resistance in rodent populations from other areas. Methods: A ranging study was conducted whereby successive groups of ship rats were administered brodifacoum doses that were increased or decreased progressively, until an International Normalised Ratio (INR) of 3.6 was reached. Linear regression was used to model the relationship between dose and INR, and ED50 dose was estimated using the resulting model. Results: None of the rats appeared susceptible to brodifacoum at previously reported LD50 exposures for this species. The ED50 of brodifacoum was estimated to be 2.88 mg/kg for males and 3.81 mg/kg for females. These values are 6-8 times greater than the previously published lethal dose values for ship rats in New Zealand. Conclusions: Blood-clotting inhibition was detected in the rats only following high doses of brodifacoum, which may indicate resistance within the sampled population. Implications: Relatively low susceptibility, or resistance, to brodifacoum in New Zealand ship rats may be mediated by spatial connections between areas with different histories and patterns of anticoagulant rodenticide use.
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    Combining prior and post-release data while accounting for dispersal to improve predictions for reintroduction populations
    (John Wiley & Sons, Inc. on behalf of Zoological Society of London., 2024-05-24) Armstrong DP; Stone ZL; Parlato EH; Ngametua G; King E; Gibson S; Zieltjes S; Parker KA; Ewen J; Canessa S
    Attempts to reintroduce species to managed areas may be compromised by dispersal into the surrounding landscape. Therefore, decisions regarding the selection and ongoing management of reintroduction areas require predicting dispersal as well as the survival and reproduction rates of the species to be reintroduced. Dispersal can potentially be measured directly by tracking animals, but this is often impractical. However, dispersal can also be inferred from re-sighting surveys done within reintroduction areas if such data are available from multiple areas with varying connectivity to the surrounding landscape, allowing apparent survival and recruitment to be modelled as a function of connectivity metrics. Here, we show how data from 10 previous reintroductions of a New Zealand passerine, the toutouwai (Petroica longipes), were used to predict population dynamics at a predator-controlled reintroduction area with high connectivity, and predictions then updated using post-release data. Bayesian hierarchical modelling of the previous data produced prior distributions for productivity, adult survival and apparent juvenile survival rates that accounted for random variation among areas as well as rat density and connectivity. The modelling of apparent juvenile survival as a function of connectivity allowed it to be partitioned into estimates of survival and fidelity. Bayesian updating based on post-release data produced posterior distributions for parameters that were consistent with the priors but much more precise. The prior data also allowed the recruitment rate estimated in the new area to be partitioned into separate estimates for productivity, juvenile survival and juvenile fidelity. Consequently, it was possible to not only estimate population growth under current management, but also predict the consequences of reducing the scale or intensity of predator control, facilitating adaptive management. The updated model could then be used to predict population growth as a function of the connectivity and predator control regime at proposed reintroduction areas while accounting for random variation among areas.
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    Mixed Mating in a Multi-Origin Population Suggests High Potential for Genetic Rescue in North Island Brown Kiwi, Apteryx mantelli
    (Frontiers Media S.A., 2021-08-10) Undin M; Lockhart PJ; Hills SFK; Armstrong DP; Castro I; Berger-Tal O
    Reinforcement translocations are increasingly utilised in conservation with the goal of achieving genetic rescue. However, concerns regarding undesirable results, such as genetic homogenisation or replacement, are widespread. One factor influencing translocation outcomes is the rate at which the resident and the introduced individuals interbreed. Consequently, post-release mate choice is a key behaviour to consider in conservation planning. Here we studied mating, and its consequences for genomic admixture, in the North Island brown kiwi Apteryx mantelli population on Ponui Island which was founded by two translocation events over 50 years ago. The two source populations used are now recognised as belonging to two separate management units between which birds differ in size and are genetically differentiated. We examined the correlation between male and female morphometrics for 17 known pairs and quantified the relatedness of 20 pairs from this admixed population. In addition, we compared the genetic similarity and makeup of 106 Ponui Island birds, including 23 known pairs, to birds representing the source populations for the original translocations. We found no evidence for size-assortative mating. On the contrary, genomic SNP data suggested that kiwi of one feather did not flock together, meaning that mate choice resulted in pairing between individuals that were less related than expected by random chance. Furthermore, the birds in the current Ponui Island population were found to fall along a gradient of genomic composition consistent with non-clustered representation of the two parental genomes. These findings indicate potential for successful genetic rescue in future Apteryx reinforcement translocations, a potential that is currently under utilised due to restrictive translocation policies. In light of our findings, we suggest that reconsideration of these policies could render great benefits for the future diversity of this iconic genus in New Zealand.