Defining reintroduction success using IUCN criteria for threatened species: a demographic assessment A. Robert 1 , B. Colas 2 , I. Guigon 1 , C. Kerbiriou 3 , J-B. Mihoub 4 , M. Saint-Jalme 1 & F. Sarrazin 3 1 CESCO, UMR 7204, MNHN-CNRS-UPMC, Muséum National d’Histoire Naturelle, Paris, France 2 Univ. Paris Diderot, Sorbonne Paris Cité, ESE, UMR 8079, UPS-CNRS-AgroParisTech, Univ. Paris Sud 11, Orsay, France 3 CESCO, UMR 7204, MNHN-CNRS-UPMC, Université Pierre et Marie Curie, Paris, France 4 UFZ – Helmholtz Centre for Environmental Research, Leipzig, Germany Keywords reintroductions; conservation translocations; population dynamics; extinction; IUCN; population viability analysis; threatened species. Correspondence Alexandre Robert, CESCO, UMR 7204, MNHN-CNRS-UPMC, Muséum National d’Histoire Naturelle, 55, Rue Buffon, 75005 Paris, France. Tel: 33 1 40 79 57 27; Fax: 33 1 40 79 38 35; Email: arobert@mnhn.fr Editor: Iain Gordon Associate Editor: Rob Slotow Received 17 July 2014; accepted 25 November 2014 doi:10.1111/acv.12188 Abstract Despite recent efforts to develop the science of reintroduction biology, there is still no general and broadly accepted definition of reintroduction success. We investi- gate this issue based on the postulates (1) that successful reintroduction programs should produce viable populations and (2) that reliable assessments of ultimate success require that populations have reached their regulation phase. We assessed if the viability of these reintroduced populations could be evaluated using the same criteria as for remnant populations, such as the Internation Union for Conserva- tion of Nature (IUCN) Red List criteria. Using modeling, we projected the viabili- ties of theoretical populations with various life history and environmental characteristics and we tested whether population sizes (criterion D of the IUCN) and other potential predictors are relevant proxies of the risk of extinction (crite- rion E of the IUCN) in the case of remnant populations with an unknown past history and in the case of reintroduced populations that have reached their car- rying capacity. We found that, as for remnant populations, population size can be used as a relevant indicator (although subject to considerable uncertainty) of the viability of reintroduced populations. However, the results demonstrate the importance of the reintroduction failure filter, that is, the fact that the reintro- duced populations that have successfully reached their carrying capacity are those with the highest and more stable growth rates, especially if populations have been reintroduced with a few individuals. As a consequence, the general relationship between the current size of a population and its projected viability will, most likely, differ considerably between remnant and reintroduced populations. Overall, our results demonstrate that there are no theoretical limitations on the application of some of the criteria widely used for remnant populations to define reintroduction success, although these criteria are very conservative for reintro- duced populations and might be rescaled to account for the demographic filter that early extinction constitutes for these populations. Introduction Reintroduction research has long been based on descriptive or opportunistic studies (Seddon, Armstrong & Maloney, 2007), but attempts are underway to adopt a more integra- tive, standardized and theoretically sound approach to reintroductions and other conservation translocations (e.g. assisted colonizations; IUCN/SSC, 2013) to improve project outcomes and contribute to fundamental ecological research (Sarrazin & Barbault, 1996; Armstrong & Seddon, 2008). One particularly important issue is the quantification of the roles of the various intrinsic, environmental and man- agement factors on conservation translocation success, which in turn requires a standardized definition of success. However, there are still no general and broadly accepted success criteria (Sarrazin & Barbault, 1996; Fischer & Lindenmayer, 2000; Sutherland et al., 2010). Most authors consider that reintroduction programs should aim at estab- lishing viable populations (Armstrong & Seddon, 2008; Schaub et al., 2009; IUCN/SSC, 2013). However, while rein- troduction failures are generally easy to identify (e.g. docu- mented extinction of the released stock and their offspring), neither conceptual framework nor criteria are unanimously used to define the bounds of viability. The notion of population viability is, nevertheless, at the core of conservation research and long-term viability is one of the most universal and important concepts considered to define the conservation status of remnant populations (Beissinger & McCullough, 2002). Several conservation agencies have developed assessment protocols based on Animal Conservation. Print ISSN 1367-9430 Animal Conservation •• (2015) ••–•• © 2015 The Zoological Society of London 1