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The rate of biodiversity loss is not slowing despite global commitments, and the depletion of animal species can reduce the stability of ecological communities. Despite this continued loss, some substantial progress in reversing defaunation is being achieved through the intentional movement of animals to restore populations. We review the full spectrum of conservation translocations, from reinforcement and reintroduction to controversial conservation introductions that seek to restore populations outside their indigenous range or to introduce ecological replacements for extinct forms. We place the popular, but misunderstood, concept of rewilding within this framework and consider the future role of new technical developments such as de-extinction.

With recent increases in the numbers of species reintroduction projects and reintroduction-related publications, there is now a recognizable field of reintroduction biology. Nevertheless, research thus far has been fragmented and ad hoc, rather than an organized attempt to gain reliable knowledge to improve reintroduction success. We reviewed 454 recent (1990-2005) peer-reviewed papers dealing with wildlife reintroductions from 101 journals. Most research has been retrospective, either opportunistic evaluations of techniques or general project summaries, and most inference is gained from post hoc interpretation of monitoring results on a species-by-species basis. Documentation of reintroduction outcomes has improved, however, and the derivation of more general principles via meta-analyses is expected to increase. The fragmentation of the reintroduction literature remains an obstacle. There is scope to improve reintroduction biology by greater application of the hypothetico-deductive method, particularly through the use of modeling approaches and well-designed experiments. Examples of fruitful approaches in reintroduction research include experimental studies to improve outcomes from the release of captive-bred animals, use of simulation modeling to identify factors affecting the viability of reintroduced populations, and the application of spatially explicit models to plan for and evaluate reintroductions. We recommend that researchers contemplating future reintroductions carefully determine a priori the specific goals, overall ecological purpose, and inherent technical and biological limitations of a given reintroduction and that evaluation processes incorporate both experimental and modeling approaches. We suggest that the best progress will be made when multidisciplinary teams of resource managers and scientists work in close collaboration and when results from comparative analyses, experiments, and modeling are combined within and among studies.

1. Landscape connectivity, the ability of species to move between different elements of a landscape, has been evaluated mainly by expert opinion, proxy data or homing experiments, all of which have major limitations. Cost distance modelling can overcome these limitations, but the resistance values of different landscape elements are difficult to estimate. 2. Here, we present a novel method combining step selection functions with cost distance modelling to assess functional landscape connectivity. Instead of relying on movement metrics, the method uses a case-control design to assess whether the chosen steps differ from a random sample of alternatives of similar lengths. Alternative models of landscape connectivity and dispersal behaviour are represented as maps of resistance values, and compared using an information-theoretic approach to select those hypotheses that maximize the discrepancy between chosen steps and random alternatives. 3. We applied this method to daily locations recorded along the dispersal paths of 38 juvenile North Island robins Petroica longipes in a fragmented pastoral landscape in New Zealand. We compared models with different resistance values for four recognized vegetation types in the landscape and assessed gap-crossing behaviour by changing the resistance value of pasture as a function of distance to the closest woody vegetation. 4. Model comparison showed that juvenile robins move in decreasing order of preference through native forest, plantations and shrubland, and showed a marked reluctance for flying over pasture. Under the best model, the largest gap crossed was 110 m. 5. Synthesis and applications. In combination with data on the total cost distances travelled by dispersers, cost distance models of landscape connectivity can be used to predict distributions of dispersal distances in any landscape with similar vegetation types. They can therefore predict responses of species to landscape management or predict spatial dynamics of populations following reintroduction. Our method is potentially applicable to any dispersal data, even with a relatively small number of locations recorded in complex landscapes, meaning models can be fitted to data that cannot be analysed using previous method. Tools are freely available for download to allow researchers and wildlife managers to apply our methods to their own data.

Habitat disturbance is a significant factor contributing to biodiversity decline worldwide. Amphibians are particularly vulnerable because of their specific microclimatic and microhabitat requirements. In Aotearoa New Zealand, Archey’s frogs (Leiopelma archeyi) have shown some degree of resilience to severe habitat disturbance historically. However, it is unknown how much L. archeyi populations are currently being impacted by historical and ongoing mining activities and development within their range. To address this issue, we conducted paired-sample abundance estimation of L. archeyi in two areas of the Coromandel Peninsula, Te Ika-a-Māui. Sixteen pairs of 100-m² sites (i.e. sites < 100 m from one another) were surveyed, each comprising of an area which had been disturbed (at least 50% of vegetation removed) by mining exploration or urbanisation during the past 40 years and an area that remained undisturbed over the same period of time. Disturbed sites were subdivided into three categories (1980s, 1990s, and 2020–2016) based on the time elapsed since disturbance. At each site, we performed capture-recapture of frogs over three nights, using their natural markings to identify individuals. We then used a purpose-built closed mark-recapture model to estimate frog abundance. Frog abundances varied among sites but were unrelated to the history of habitat disturbance. Rather, abundance was correlated with higher elevation and with plant species typically associated with mature forest, which was present in both disturbed and undisturbed sites. Ordination techniques used to assess vegetation composition revealed variation among sites that possibly reflects forest succession and replanting in disturbed areas. From our observations, if habitat disturbance does occur we recommend allowing sites to naturally regenerate or to plant species that contribute to leaf litter depth, microhabitat complexity, and increased moisture to promote recolonisation of sites by L. archeyi.

Invasive-predator control can be beneficial to native species, but it is important to quantify those benefits to ensure they justify the costs. In a previous study (2005–2011), a modified before-after-control-impact (BACI) design was used to estimate the effect of rat control in farmland forest fragments on vital rates of North Island robins (Petroica longipes), a New Zealand native bird species often targeted in private restoration initiatives. Based on the results, continuous rat control was implemented in 5 fragments predicted to have a high probability of subpopulation growth. Here, I report subsequent abundance estimates; the number of robins in those fragments increased from 57 to 134, from 2011–2014, closely matching the prediction of 131 based on the previous vital rate estimates. In comparison, numbers declined or stayed relatively stable over this period in 8 non-controlled fragments, except for 1 fragment that was adjacent to 1 of the controlled fragments and therefore would have received juveniles dispersing from it. Therefore, the results illustrate that where there is uncertainty about where to conduct control operations, short-term data on survival and reproduction can be used to predict longer-term effects, allowing predator-control efforts to be done strategically.

The Hochstetter’s frog (Leiopelma hochstetteri) is a nationally At Risk – Declining species, but management decisions for this species are limited by the lack of established monitoring protocols and analytical methods. We compared methods for inferring spatial and temporal patterns in abundance on Aotea (Great Barrier Island) using count data collected from fifteen 100 m stream transects in 2012, 2015 and 2021. Each transect was surveyed 2–3 times on the same day each year. Frogs were not marked, but individuals were identified in 2021 based on their body sizes and locations to facilitate the use of closed-population capture-mark-recapture (CMR) methods. We compared patterns in abundance estimates derived from Bayesian formulations of CMR (2021 only), N-mixture, Poisson regression of single counts, and occupancy models. Abundance estimates from CMR and N-mixture models were realistic and reasonably precise if detection probability (p) was assumed constant among transects. N-mixture estimates were 17% lower than CMR estimates but closely correlated with them. Relaxing the assumption of constant p among transects made little difference to CMR estimates but greatly reduced the precision of N-mixture estimates. Assuming constant p among transects, the N-mixture abundance estimates for the 15 transects were consistent among years. The 95% credible interval for the change in abundance from 2012–2021 ranged from a 24% decrease to a 10% increase. Mean first counts were 32% as high as N-mixture estimates, reflecting the estimated detection probability for first surveys. However, the spatial and temporal patterns inferred from single counts were consistent with those from N-mixture, and the change over time was estimated with only slightly lower precision. Estimated occupancy probabilities were correlated with N-mixture estimates but could not distinguish among transects with greater than 50 frogs and could not be used to infer changes over time.

Notes how introducing species to areas outside their historical range to secure their future under climate change is a controversial strategy for preventing extinction. Develops the first rigorous quantitative framework for deciding whether or not a particular introduction should go ahead, which species to prioritize for introduction, and where and how to introduce them. Applies the framework to a case study of tuatara (Sphenodon punctatus) in New Zealand, considering introducing tuatara from the well-studied and genetically distinct North Brother Island population to a single location: a hypothetical mainland sanctuary on New Zealand’s South Island (with a higher latitude and cooler climate). Source: National Library of New Zealand Te Puna Matauranga o Aotearoa, licensed by the Department of Internal Affairs for re-use under the Creative Commons Attribution 3.0 New Zealand Licence.

Introductions of mammalian predators have led to extinctions or declines of many species on islands; hence eradications of these mammals have played a major role in biodiversity conservation. However, eradications are costly and sometimes controversial. It is therefore important to conduct carefully designed sampling programmes that allow benefits to native species to be quantified. We report the results of sampling conducted in 1994–1996 and 2014–2015 to estimate changes in relative abundance of lizards on Kāpiti Island over 20 years following the eradication of Norway rats (Rattus norvegicus) and kiore (Rattus exulans) in 1996. Sampling was conducted in five different habitats over the island, and in each habitat involved repeatedly sampling 4–5 pitfall stations (five pitfall traps each) and conducting spotlighting and daytime searches along 2–3 transect lines. We used generalised linear mixed modelling to estimate proportional changes in lizard encounter rates while accounting for effects of month, weather variables, and changes in vegetation density. Pitfall capture rates for northern grass skinks (Oligosoma polychroma), brown skinks (Oligosoma zelandicum), and copper skinks (Oligosoma aeneum) were estimated to increase 2- to 28-fold in habitats where they were detected in 1994–1996, and these species were also found in 2014–2015 in habitats where they were not detected in 1994–1996. Spotlighting encounter rates for geckos (predominantly Raukawa geckos, Woodworthia maculata) were estimated to increase 3.7-fold between the two time periods. There were sparse observations of ornate skinks (Oligosoma ornatum), forest geckos (Mokopirirakau granulatus) and Wellington green geckos (Naultinus punctatus), whereas goldstripe geckos (Woodworthia chrysosiretica), which were discovered on the island in 2013, were not detected in the areas sampled. Most lizards continue to be found in habitats with low, dense vegetation, a pattern that may be at least partially attributable to predation pressure from the abundant weka (Gallirallus australis) on the island.

A key goal of ecological research is to obtain reliable estimates of population demographic rates, abundance and trends. However, a common challenge when studying wildlife populations is imperfect detection or breeding observation, which results in unknown survival status and reproductive output for some individuals. It is important to account for undetected individuals in population models because they contribute to population abundance and dynamics, and can have implications for population management. Promisingly, recent methodological advances provide us with the tools to integrate data from multiple independent sources to gain insights into the unobserved component of populations. We use data from five reintroduced populations of a threatened New Zealand bird, the hihi (Notiomystis cincta), to develop an integrated population modelling framework that allows missing values for survival status, sex and reproductive output to be modelled. Our approach combines parallel matrices of encounter and reproduction histories from marked individuals, as well as counts of unmarked recruits detected at the start of each breeding season. Integrating these multiple data types enabled us to simultaneously model survival and reproduction of detected individuals, undetected individuals and unknown (never detected) individuals to derive parameter estimates and projections based on all available data, thereby improving our understanding of population dynamics and enabling full propagation of uncertainty. The methods presented will be especially useful for management programmes for populations that are intensively monitored but where individuals are still imperfectly detected, as will be the case for most threatened wild populations.

1. Adaptive management involves the development of predictive models, strategic manipulation of management actions to gain information, and subsequent updating of the models and management. The paradigm has several characteristics that make it an effective approach for determining requirements of re-introduced populations. 2. Adaptive management was applied to the re-introduction of hihi Notiomystis cincta, a New Zealand forest bird that had been reduced to a single island population. Following three previous failed re-introductions, we initiated an 8-year series of management manipulations when hihi were re-introduced to Mokoia Island in 1994. 3. We developed a population model for projecting outcomes under potential management scenarios, and updated it on an annual basis. The population model combined submodels for survival and reproduction that were selected from sets of candidate models using an information-theoretic approach. All projections incorporated demographic stochasticity, and later projections incorporated uncertainty associated with model selection and parameter estimation. 4. The programme showed that some actions (e.g. the provision of sugar water during breeding season and mite control) substantially increased the population's growth rate, but that persistence was uncertain under any management scenario. The population growth rate was shown to be constrained by a low adult survival rate that was unaffected by supplementary feeding, and was associated with a feature of the island (high density of Aspergillus fumigatus spores) that could not be remedied by management. Hihi were therefore removed from Mokoia. However, the management actions shown to be effective on Mokoia have now been used to produce sustained growth in three other re-introduced hihi populations. 6. Synthesis and applications. The results illustrate how adaptive management can facilitate successful species recovery. Without manipulation of management treatments, the Mokoia hihi re-introduction would have just been another failure that provided no useful information. Instead, our manipulations allowed us to identify effective management actions that were successfully applied to other re-introduced populations, and allowed us to identify a limiting factor that had not been previously considered. We have illustrated how other characteristics of the adaptive management approach (flexible treatments, ongoing monitoring, early model development, quantitative projections and incorporation of uncertainty) were essential to the programme.