Animal reintroductions: An innovative assessment of survival
Introduction
Over the last several decades, methodologies targeted specifically at species preservation have flourished. The family of tools termed relocation, repatriation, translocation, and reintroduction represent an approach to managing populations and species of concern that focus on moving individuals or groups of individuals from established populations (wild or captive) to historical or new habitat in response to threats ranging from habitat loss to population decline as a result of disease (Seigel and Dodd, 2002, Dodd, 2005). Despite ongoing use of this management tool (hereafter reintroduction), success is rare. Reintroduction efforts for birds, mammals, and fish are deemed successful less than 50% of the time (Griffiths et al., 1989, Harig and Fausch, 2002). Reintroduction efforts for amphibians and reptiles reflect similar results, for example, of 85 projects considered by Germano and Bishop (2008), 42% were considered successful. Griffiths and Pavajeau (2008) considered 58 projects that included reintroduction of amphibians and were able to assess 22 for success, of these; only 13 were considered highly successful. However, success can be defined on a continuum from survival of released individuals (low success, Griffiths and Pavajeau, 2008) to the establishment of a breeding population of adults and the presence of multiple age classes (high success, Griffiths and Pavajeau, 2008, Semlitsch, 2001, Dodd and Seigel, 1991) and because negative results are less likely to be published (Fanelli, 2012), the proportion of successful reintroductions is likely inflated.
Reintroduction efforts can have high stakes. Efforts are costly but may be critical to the persistence of the species. Endpoints can be elusive and typically, efforts suffer from lack of quantification and monitoring (Seigel and Dodd, 2002, Dodd, 2005, Field et al., 2007). Scenarios with high stakes, whether financial, or biological (i.e., the extinction of a species), call for accurate evaluations of reintroduction effort. Success depends on multiple factors, including habitat quality and the number of individuals that are released, and many of these attributes or characteristics can be quantified, allowing for an evaluation of effort. Despite this need, quantitative evaluations of reintroduction efforts are uncommon (but see Bell et al., 2004). Furthermore, reintroduction efforts provide an appropriate context (ongoing decisions and a high degree of uncertainty) within which managers can apply adaptive management methods (Runge, 2011). In particular, the Decision-Theoretic School (DTS) of adaptive management (Williams et al., 2007, Runge, 2011) uses formal tools for decision analysis but also incorporates predictive modeling (with ongoing updates from monitoring) and articulates levels of uncertainty. The identification of appropriate benchmarks to measure progress (Dodd, 2010) and a quantification of these elements prior to the completion of a reintroduction project offer an opportunity to assess and potentially re-direct conservation efforts. Information gleaned from incremental assessments can provide defensible estimates of biological success (e.g., survivorship of a release effort), identify potential cost savings (thereby increasing accountability), and importantly, provide insight into what “success” might look like in the particular situation.
Reintroduction is likely to be particularly important for conservation of amphibian species because of the increasing number of species brought from the wild into “assurance colonies” to protect them from acute threats such as disease that can presage likely extinction in the wild (e.g., Mendelson et al., 2006, Zippel et al., 2011). Such programs provide respite in the short term but maintenance of biodiversity in the long run requires returning animals to their native, or suitable new, habitat with subsequent successful natural reproduction.
Program initiation, implementation, and final outcomes are all topics that have been discussed thoroughly elsewhere (Dodd and Seigel, 1991, Denton et al., 1997, Griffiths and Pavajeau, 2008, Lukis, 2009). Instead, we focus here on measuring the progress of a reintroduction program, specifically survival of a particular life stage, using a novel application of the multi-state, robust design, capture–recapture model. Our focus on progress is unique; intermediate assessments of ongoing efforts are generally overlooked but can inform husbandry and colony maintenance, judge the short-term efficacy of release methods, determine the duration of efforts necessary before success is achieved, and importantly, refine plans for funding acquisition – all of which can provide foundational data for structured decision making and adaptive management strategies.
Intermediate assessment of reintroduction success (i.e., progress) could address any life stage between release and breeding age and may focus on a variety of questions specific to the situation and the natural history of the target species. For example, an informative question might be: How many of the released tadpoles survive to metamorphosis? An answer to this question provides data to use in calculating the cost of the introduction as well as an indication of the robustness of the tadpoles which may inform husbandry efforts. Moreover, these short-term results can inform, temper, and revise the time frame needed to meet long-term reintroduction goals. For example,understanding survival at each life stage can inform one of the most common questions in conservation biology and reintroduction activities; namely, how many released animals are required to provide the founding genetic material needed to capture most of the available genetic diversity and avoid the genetic pitfalls of small populations (e.g., Jamieson and Lacy, 2012, Zeisset and Beebee, 2012, Deredec and Courchamp, 2007, Soule and Wilcox, 1980).
Assessing a reintroduction effort is different in focus from typical monitoring exercises because information beyond occurrence and abundance is needed. Rigorous methods to quantitatively assess amphibian reintroductions are sparse and untested particularly in high elevation, sub-alpine environments. We present results from an ongoing reintroduction effort of Boreal Toads (Anaxyrus [Bufo] boreas) in such an environment in Rocky Mountain National Park, Colorado (Fig. 1) to illustrate how intermediate results can inform next steps. We (1) describe initial site selection; (2) quantify survival in eggs collected from the wild versus those produced in captivity; and (3) quantify survival to metamorphosis (i.e., over summer survival) of released tadpoles using removal sampling.
Section snippets
Study species
Boreal Toads are an endangered species in Colorado and have been petitioned for federal listing (Greenwald et al., 2011). They are also considered one of the top 10 most vulnerable amphibians and reptiles in the U.S. (Giese, 2013). The Boreal Toad is one of only four extant amphibian species in Rocky Mountain National Park (RMNP, northeastern Colorado) (Corn et al., 1997). These toads belong to the A. boreas species group but the toads in the southern Rocky Mountains likely represent a
Data analysis
We used the data collected above (2010–2013) to construct capture histories for each released individual, consisting of three primary periods (initial release, first removal sample, final removal sample) and two states (Td = tadpoles, M = metamorphs). Recaptures during the final removal were distributed randomly among histories from the marked cohort obtained during the first removal sample such that parameter estimates were not biased (Converse et al., 2008).
We analyzed capture history data from
Site selection and disease surveillance
The Red Mountain site was selected based primarily on criteria set forth by the Boreal Toad Recovery Team (Loeffler, 2001): (1) historical evidence of Boreal Toads in the area (Corn et al., 1997); (2) chorus frogs were the only amphibian present and this species often co-occurs with Boreal Toads; (3) no known Boreal Toad breeding populations were within 5 km; (4) no evidence of disease: ranavirus has not been detected in any amphibians in RMNP (Green and Muths, 2004) and while Bd has been
Discussion
Our goal was to describe the progress of this reintroduction effort, not to declare success or failure, which indeed, we cannot do at this point in the reintroduction program. Specifically, we have evidence of survival beyond metamorphosis which was lacking from earlier work. We note that research over the last 10 years has rendered some aspects of the boreal toad recovery plan (developed in 2001) either obsolete or moot. For example, requiring reintroductions to be isolated from extant sites
Conclusions
We assessed an ongoing effort to reintroduce Boreal Toads. We provide evidence for the efficacy of a novel application of a multistate robust-design model (using batch marks) to estimate survival of a critical life stage of this species indicating that defensible quantification of survival of metamorphs is possible. This is important from a natural history perspective because there are few studies that report demographic estimates, or attempt to track the activity of post-hatching, but
Acknowledgments
R. Scherer contributed statistical insights. We thank E. Davinroy, J. Marrinan, and T. Smith from CPW-NASRF and numerous technicians and volunteers. Members of the Hoke-Funk laboratory at CSU provided comments that improved the manuscript. All methods were approved by the USGS Animal Care Committee. This is contribution no. 470 of the USGS Amphibian Research and Monitoring Initiative. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the
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