Using Bayesian mark-recapture modelling to quantify the strength and duration of post-release effects in reintroduced populations

Abstract

Translocated animals often suffer elevated mortality during some acclimation period after release. Such post-release effects must be accounted for when estimating normal survival rates and therefore predicting population persistence. The standard approach for doing this is to nominate a fixed acclimation period, and either i) exclude survival data over that period, or ii) use model selection criteria to test whether survival differs over that period. We present a more flexible approach where the acclimation period is treated as unknown and is estimated simultaneously with the pre-and post-acclimation survival probabilities. We illustrate this approach using survival data for six reintroduced populations involving three New Zealand forest bird species. Analyses of the complete data sets (22-73 surveys conducted over 4-14 years) indicated that significant post-release effects occurred in at least one sex in five of the six populations, with 30-84% mortality attributable to post-release effects over acclimation periods ranging from 1-9 months. When we applied the approach to just the first year of data for each population, the estimated normal survival rates were consistent with those obtained from the complete data sets, and always at least as accurate as our previous approach of excluding data up to the next breeding season after translocation. The flexible approach therefore appears to be effective for accounting for post-release effects in survival estimation, and is beneficial in quantifying both the strength and duration of those effects so that pre-and post-release management strategies are better informed.

Making structured decisions for reintroduced populations in the face of uncertainty

“…The BP population declined over the first 2 years due to poor initial survival of the reintroduced females (only four of 21 females survived the first 6 months), but modeling projections suggested that this was due to transient effects of the translocation (cost of release effects; Armstrong et al, 2017) and that more stable site based vital rates would allow the population to persist (Panfylova, Bemelmans, Devine, Frost, & Armstrong, 2016). The 44 birds released were from Tiritiri Matangi (TM) Island, which is currently considered the only possible source population.…”

Survival cost to relocation does not reduce population self‐sustainability in an amphibian

“…For example, survival immediately following the release of animals into new habitat affects the outcome of a relocation (i.e., establishment phase, Armstrong and Seddon , Armstrong et al. ). Reduced survival during the establishment phase occurs in a range of vertebrates (birds [Armstrong et al.…”

“…Reduced survival during the establishment phase occurs in a range of vertebrates (birds [Armstrong et al. ], mammals [Jule et al. ], reptiles [Roe et al.…”

“…, Armstrong et al. ) and is influenced by multiple factors. Physiological (chronic or acute) stress response, typically associated with animal capture, transport, and relocation, can result in a reduced survival after relocation (Dickens et al.…”

“…Environmentally‐induced changes in individual phenotype, called “acclimatization” or “acclimation” (i.e., plastic phenotypic response to a stress), can increase post‐relocation survival (Armstrong et al. ). The ability of individuals to accommodate novel environmental conditions may also depend on individual factors such as sex and age (Teixeira et al.…”