Learning From the Past, Adapting to the Future: Experimental Approaches in Conservation Translocations

Abstract

Conservation translocations (hereafter ‘translocations’) have long been regarded as an important management tool for the recovery of species threatened with extinction, and their use continues to grow (Armstrong et al. 2019). Translocations can be inspirational and may stimulate fruitful and effective partnerships (Parker 2008; Fischer et al. 2023), but can also be a potential source of conflict (Consorte-McCrea et al. 2022; Glikman et al. 2023). Furthermore, translocations may entail high financial costs (Berger-Tal et al. 2020), those involving animals may be highly stressful (Dickens et al. 2010), and statistically have a high chance of failure (Morris et al. 2021). To paraphrase Axel Moehrenschlager (Chair of the IUCN/SSC Conservation Translocation Specialist Group [CTSG]), the best translocation is one that does not need to happen (Moehrenschlager 2021). Unfortunately, the reality for many imperilled species is that threat abatement alone is insufficient to reverse their fortunes or to restore ecosystem function (Seddon 2010, 2023). As an increasing number of species are considered to be threatened with extinction every year (IUCN 2024), the importance of translocations will likely continue to grow. Therefore, it is critical that those undertaking translocations not only follow but continue to push the boundaries of ‘best practice’, including communicating what they have learned (Batson et al. 2015; Maschinski et al. 2023). There is a wealth of peer-reviewed literature (Resende et al. 2020) in journals, such as Animal Conservation, along with an increasing number of books in the field of reintroduction biology, which provide a valuable accumulation of experience and knowledge.

Conferences too can play an important role in the process of knowledge-sharing. This special issue of Animal Conservation stems from the most recent International Conservation Translocation Conference (ICTC), held in Fremantle, Western Australia in November 2023. Organised on behalf of the CTSG, its theme was ‘Learning from the Past, Adapting to the Future’ and was attended by 300 delegates from six continents, with presentations on a diverse range of taxa, including vertebrates, invertebrates and plants. The articles in this special issue were originally presented at the ICTC and tackle some of the key themes in current reintroduction biology, and highlight their complexity on multiple taxa and landscapes. In this editorial, we provide an overview of the key aims and findings of the articles published in this special issue, as well as how they contribute to developing and adapting conservation translocations to meet the present and future challenges in species and ecosystem restoration.

In their article, Parlato et al. (2024) illustrate a case study in the use of structured decision-making (SDM) to support a translocation of the iconic karure/kakaruia/Chatham Island black robin (Petroica traversi). SDM is increasingly used in the context of natural resource management to help navigate complex and/or uncertain decisions. In the black robin study, the authors used SDM to ‘overcome a long-standing conservation impasse’ and illustrate a pathway to address the inherent uncertainty faced by translocation programs. They demonstrate an approach that is inclusive and transparent, and facilitates logical outcomes that are reflective of the shared values of all project partners.

A critical aspect of the SDM process is the use of predictive models to account for uncertainty around the consequences of alternative management strategies (Nichols and Armstrong 2012). Armstrong et al. (2024) demonstrate how these predictions can be improved by updating modelled priors with post-release monitoring data, as part of an adaptive management process for another species of robin from Aotearoa New Zealand, the toutouwai (Petroica longipes). Data were obtained through resightings from 10 previous reintroductions and used in a Bayesian hierarchical modelling framework to make predictions about population growth rates associated with different management alternatives. This study is the first to fully demonstrate how the adaptive management cycle can be implemented with a fully data-based approach.

Defining success in translocations remains an enduring challenge. Globally, translocation failure is not uncommon, but there is considerable variation in how ‘success’ is defined and evaluated. In their article, Cowen et al. (2024) present a retrospective critique of performance measures for translocations of two small marsupials. They found that most success criteria were able to be assessed (and met) for the Shark Bay bandicoot (Perameles bougainville), but monitoring difficulties constrained their evaluation for the dibbler (Parantechinus apicalis). The authors identified shortcomings in the way that criteria for translocations were originally conceived and advocate an SDM approach towards translocation planning, including a conceptual framework for developing meaningful performance measures.

Another important decision-support tool in the translocation toolbox is population viability analysis (PVA) (Chaudhary and Oli 2020). PVA can be used to make predictions about the demographic and genetic outcomes of translocation scenarios (Canessa et al. 2014). Faust et al. (2024) used PVA to evaluate current and future management strategies for the Puerto Rican parrot (Amazona vittata), including the effect of increasing severity/frequency of hurricanes. Although current management appears to be maintaining a low extinction risk, wild populations are apparently reliant on ongoing releases of captive-bred birds unless demographic rates can be improved. Hurricanes were predicted to have a major impact on some populations, thereby increasing their reliance on supplementations following such disturbance. As befits an adaptive management approach, the authors recommend the continual refinement of this PVA as new information becomes available.

Incorporating genetic considerations into translocation planning, particularly in small, isolated populations, is an important area in reintroduction biology (Bragg et al. 2019; Neaves et al. 2022). The Tasmanian devil (Sarcophilus harrisii) has been an important focal species for testing hypotheses around genetic management, especially in the context of managing Devil Facial Tumour Disease (DFTD), which has decimated the species. McLennan et al. (2024) demonstrated that selective reinforcement of small populations of devils resulted in an improvement in genetic and demographic metrics without a concomitant increase in DFTD prevalence. The immunological capacity of the population was also improved, resulting in better health of the population, including greater resilience to DFTD. The authors emphasised the importance of effective genetic monitoring as a key aspect of adaptive management, a cornerstone of the SDM framework.

Although incorporating genetics is a fundamental aspect of translocation planning, a lack of resources and knowledge for managers imposes a gap between data generation and application, limiting its implementation. To assist with this integration, Hogg et al. (2024) presented the Applied Conservation Genomics Hub (ACGH), an expansion of the Threatened Species Initiative (Hogg et al. 2022) and a ‘toolkit’ to support the use of genetic data in species' conservation in Australia. The authors identify key questions that may arise around the use of genetics in species conservation, and highlight relevant resources provided by the ACGH that can be used to address them. The ACGH represents an exciting development for conservation practitioners in Australia as well as globally.

Restoring an apex predator to an ecosystem requires careful planning, and Stepkovitch et al. (2023) tackle the tricky proposition of restoring a threatened apex predator, the chuditch or western quoll (Dasyurus geoffroii), to an ecosystem in Australia's arid zone containing populations of reintroduced threatened prey species. Balancing the benefits of top-down trophic cascades, particularly in the context of a fenced safe haven (e.g., prey naiveté, overabundance), with the direct impact of predation is a substantial challenge. The findings illustrate the complexity of reintroducing predators to a system where the impact of predation is influenced by a confined population and the boom-bust dynamics of prey species.

As methods to manage invasive predators such as feral cats (Felis catus) and stoats (Mustela erminea) improve, managers can contemplate translocations of sensitive species into areas where these predators may occur at lower densities. In these scenarios, it is important to understand the threshold of predator density at which the viability of a translocated population can still be maintained. In their article, Parker et al. (2024) explore density thresholds of cats and stoats for three species of bird with different degrees of vulnerability in Aotearoa New Zealand. This study demonstrates the complexity of estimating predator thresholds, especially when multiple species of predator and prey are involved, as well as the value of targeted monitoring to address uncertainty.

Similarly, if translocated populations disperse beyond areas where predators are effectively managed, this can create a source-sink dynamic which may affect the viability of the metapopulation. Stone et al. (2024) addressed uncertainty about how landscape connectivity affects dispersal and territory formation in toutouwai using post-release radio-tracking data to build species distribution models. They identified a core area of breeding habitat and, as toutouwai are most vulnerable to predation (e.g., by rats [Rattus spp.]) during the breeding season, predator control could be targeted to this core area during this period to improve survival. The authors suggest that species distribution models based on monitoring data could be used to both guide the management of existing translocation sites and facilitate new translocations.

Assisted colonisation (also called assisted migration or managed relocation) is a type of conservation introduction and may be an important management action to safeguard the existence of species threatened by climate change, but also presents significant challenges. Trewartha et al. (2024) present a case study of the pygmy bluetongue (Tiliqua adelaidensis), a small lizard whose northern populations may be negatively affected by a changing climate. The species' poor dispersal capabilities and habitat specialism make it a candidate for assisted migration. This study investigated behavioural plasticity in this species in relation to environmental variables (humidity and temperature) and found there were important differences between northern and southern populations, highlighting the potential difficulties that assisted migrations may face.

Trial translocations may be valuable initiatives to learn more about subject species and recipient ecosystems to support decision-making for full-scale projects. Emery et al. (2024) undertook trial reintroductions of two Extinct in the Wild reptile species into a semi-wild enclosure to develop and refine protocols for future translocations. The study evaluated the success of the trial and makes recommendations about improvements. It also represents a cautionary tale that short-term success may not translate in the longer term, especially if a catastrophic event occurs; in this case (spoiler alert!), an incursion of wolf snakes (Lycodon capucinus).

The ways that translocations continue to break new ground is illustrated through the methods used to reinforce an aquatic warbler (Acrocephalus paludicola) population in Lithuania (Morkvėnas et al. 2025). To ensure that juvenile warblers would return to the release site after migrating to Africa, whole broods were moved from the source site in Belarus overnight, in their original nest, to the release site in Lithuania and then hand-fed at 5–7 min intervals until fledging. Juveniles were soft-released at 30 days old, after which their presence was monitored using RFID scanners designed to detect tags attached to their leg-rings (bands). The results of this Herculean effort were the return of 22% and 12% of juveniles in the subsequent seasons (comparable to natural return rates) and the number of singing males in the population increasing from 8 to 33.

Going forward, as conservation managers and scientists work to confront the ensuing biodiversity crisis, translocations will continue to play an important role (Moehrenschlager et al. 2023). To ensure that future translocations are effective in terms of conservation, socio-economic and animal welfare outcomes, managers need to continually monitor, evaluate and adapt their approaches. Ideally, new or modified approaches are applied in an experimental framework, incorporating the latest tools and resources, and with the findings communicated to the broader translocation community. The diverse array of studies in this special issue showcases this process superbly. Collectively, these studies demonstrate how we can continue to advance the field of translocation science to ‘learn from the past and adapt to the future’ and address the biological crisis that our planet is facing.

All authors contributed to developing the paper, editing drafts and provided final approval for publication.