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.

Taxonomic bias has been documented in general science and conservation research publications. We examined whether taxonomic bias is similarly severe in actual conservation programmes as indicated by the focus of species reintroduction projects worldwide. We compiled a database of reintroduction projects worldwide, yielding a total of 699 species of plants and animals that are the focus of recent, current or planned reintroductions. Using IUCN (World Conservation Union) data for total numbers of known species worldwide, we found that vertebrate projects were over-represented with respect to their prevalence in nature. Within vertebrates, mammals and, to a lesser extent, birds, were over-represented, whereas fish were underrepresented. This over-representation extended to two mammal orders, artiodactylids and carnivores, and to four bird orders, anseriforms, falconiforms, gruiforms and galliforms. For neither mammals nor birds was reintroduction project bias related to any differences between orders in vulnerability to threat. Bird species that are the focus of reintroduction efforts are more likely to be categorised as 'Threatened' than expected on the basis of the distribution of all known species over all threat categories, however, nearly half of all bird species being reintroduced are classified as 'Least Concern'. The selection of candidates for reintroduction programmes is likely to consider national priorities, availability of funding and local community support, over global conservation status, While a focus on charismatic species may serve to garner public support for conservation efforts, it may also divert scarce conservation resources away from taxa more in need of attention.

Reintroductions and other conservation translocations are an important but often controversial form of wildlife management. Some authors have suggested the low success rates may reflect poor planning and decision-making. In this study, we used examples of herpetofaunal reintroductions, published in four volumes of the IUCN's Reintroduction Specialist Group Global Perspectives in Reintroduction Biology, to identify the objectives set by reintroduction practitioners, the indicators of success they choose and the types of difficulties they encounter. We found objectives focused on target species, but also on broader ecological objectives, such as ecosystem restoration, and social and economic aims. Practitioners reported high success rates: however, these referred to a mixture of general objectives, reflecting the fundamental aims of programmes, and technical aspects, such as developing husbandry protocols, that are important only as stepping stones for broader objectives. In some cases, important objectives were not assigned relevant indicators, thus making assessment impossible. Non-biological aspects such as funding dynamics were the most important source of difficulties; however, they were not always openly recognized by assigning relevant objectives and indicators. We argue that the adoption of a more structured approach to decision-making could help in addressing all these issues. In particular, we recommend that where possible, managers should clearly state all relevant objectives and constraints, and distinguish their respective relevance and importance. If such elements are not clearly defined a priori, planning and assessing reintroductions can become difficult or even impossible, increasing the risk of inefficient use of resources.

Humans depend on biodiversity in myriad ways, yet species are being rapidly lost due to human activities. The ecosystem services approach to conservation tries to establish the value that society derives from the natural world such that the true cost of proposed development actions becomes apparent to decision makers. Species are an integral component of ecosystems, and the value they provide in terms of services should be a standard part of ecosystem assessments. However, assessing the value of species is difficult and will always remain incomplete. Some of the most difficult species' benefits to assess are those that accrue unexpectedly or are wholly unanticipated. In this review, we consider recent examples from a wide variety of species and a diverse set of ecosystem services that illustrate this point and support the application of the precautionary principle to decisions affecting the natural world.

Reintroduction of animals is becoming increasingly popular as a means of restoring populations of threatened species. Sometimes depletion of wild populations leaves only captive populations from which reintroduction projects can obtain founders for releases. The World Conservation Union guidelines on reintro-ductions recommend that the individuals to be reintroduced should be of the same subspecies as those that were extirpated. In some cases, however, a subspecies may have become extinct in the wild and in captivity. A substitute form may then be chosen for possible release. Such substitutions are actually a form of benign introduction. Considerations include assessment of the value of a substitution project and the selection of a suitable substitute. Species substitutions increase biodiversity, conserve related forms, improve public awareness of conservation issues, educate the public, and may be implemented for aesthetic or economic reasons. Selection of a suitable substitute should focus on extant subspecies and consider genetic relatedness, phenotype, ecological compatibility, and conservation value of potential candidates. An example of a substitution project is the reintroduction of the North African Red-necked Ostrich ( Struthio camelus camelus ) into areas once occupied by the now extinct Arabian Ostrich ( Struthio camelus syriacus ). S. c. camelus was chosen as a substitute because of its geographic proximity, phenotypic similarity, and conservation value. The World Conservation Union's reintroduction guidelines should be consulted before a project is begun. Bases para la Substitución Subespecífica en Proyectos de Restauración de Vida SilvestreResumen: La reintroducción de animales se ha vuelto muy popular como una medida para restaurar poblaciones de especies en peligro. Algunas veces la disminución de poblaciones silvestres deja unicamente poblaciones cautivas a partir de las cuales los proyectos de reintroducción pueden obtener los fundadores para sus liberaciones. Las bases de la Unión para la Conservación Mundial en materia de reintroducciones recomienda que los individuos a ser reintroducidos deben ser de la misma subespecie que aquellos que fueron extirpados. Sin embargo, en algunos casos, una subespecie puede haberse extinguido tanto en su hábitat como en cautiverio. Una forma substituta puede ser escogida para una posible liberación. Substituciones de este tipo son de hecho una forma benigna de introducción. Las consideraciones incluyen la evaluación de el valor de un proyecto de substitución y la selección de un substituto apto. La substitución de especies incrementa la biodiversidad, conserva las formas relacionadas, mejora la conciencia del público en asuntos de conservación, educa al público y puede ser implementada por razones estéticas o económicas. La selección de un substituto apto debe enfocarse en subespecies existentes y considerar la relación genética, fenotipo, compatibilidad económica y valor de conservación de los candidadtos potenciales. Un ejemplo de un proyecto de substitución...

Vipers are among the most misunderstood and persecuted animals. They occupy most terrestrial ecosystems around the world, often at high population densities. However, certain aspects of their biology (e.g., low fecundity and slow growth) have resulted in vipers being disproportionately threatened by extinction. Despite increased extinction risk, relatively little is known about viper biology, severely limiting the development and implementation of conservation initiatives. Here, we review the conservation status of vipers globally, map species richness, and develop three indices (one reactive; one proactive; one combined index emphasising irreplaceable species facing severe threats) to identify species for which conservation action should be prioritised. Moreover, we map species richness weighted by each index to identify regions for conservation prioritisation. We ranked prioritisation scores for all species for which data were available. In doing so we identify species for which valuable data are missing and that should be prioritised for research. We additionally show that 17 species, currently listed as Not Assessed or Data Deficient by the IUCN, score sufficiently high on our Threat Index to be considered as Threatened in the future. We identify multiple regions for which viper conservation action should be prioritised. These areas broadly correlate with species richness patterns, suggesting that species richness may be an effective proxy for conservation planning. Finally, we discuss the major gaps in knowledge, as well as the major threats facing vipers.

Article impact statement: Conservation triage is not necessary for species conservation. Adequate resources exist; even species with small populations can recover.

Simple Summary: Acting to preserve biodiversity can involve harming individual animals. It has recently been argued that conventional practice has placed too much emphasis on the preservation of collective entities, such as populations and species, at the expense of suffering for individuals. At least some advocates of the 'Compassionate Conservation' movement find any deployment of lethal measures in the interests of conservation to be unacceptable. This shifts the balance of priorities too far. While conservationists have a duty to minimise harm, and to use non-lethal measures where feasible, there will be serious implications for conservation if this movement were to be widely influential. Furthermore, the 'do-no-harm' maxim the compassionate conservationists advocate does not always promote the welfare of individual animals.Abstract: Human activity affecting the welfare of wild vertebrates, widely accepted to be sentient, and therefore deserving of moral concern, is widespread. A variety of motives lead to the killing of individual wild animals. These include to provide food, to protect stock and other human interests, and also for sport. The acceptability of such killing is widely believed to vary with the motive and method. Individual vertebrates are also killed by conservationists. Whether securing conservation goals is an adequate reason for such killing has recently been challenged. Conventional conservation practice has tended to prioritise ecological collectives, such as populations and species, when their interests conflict with those of individuals. Supporters of the 'Compassionate Conservation' movement argue both that conservationists have neglected animal welfare when such conflicts arise and that no killing for conservation is justified. We counter that conservationists increasingly seek to adhere to high standards of welfare, and that the extreme position advocated by some supporters of 'Compassionate Conservation', rooted in virtue ethics, would, if widely accepted, lead to considerable negative effects for conservation. Conservation practice cannot afford to neglect consequences. Moreover, the do-no-harm maxim does not always lead to better outcomes for animal welfare.