Avian Conservation and Ecology (Dec 2022)
Survival of translocated Columbian Sharp-tailed Grouse: recognizing trends in post-release mortality to improve reintroductions
Abstract
Survival of translocated prairie-grouse (Tympanuchus spp.) is often low in the first few weeks or months following release into a novel environment. Understanding the processes and mechanisms that influence short-term, post-release survival, such as Allee effects (i.e., inverse density dependence), or individual characteristics of translocated individuals (e.g., age, sex) is imperative for designing successful translocation programs. Additionally, identifying timeframes during which translocated individuals are particularly vulnerable to mortality is especially useful for population management. We translocated 215 Columbian Sharp-tailed Grouse (T. phasianellus columbianus; CSTG) as a species reintroduction project to historical habitat in northeastern Nevada from 2013 to 2017 and quantified annual post-release survival probabilities during the 150-d breeding season. In a Bayesian framework, we first identified a prospective 40-d threshold in which the daily probability of survival substantially increased from before to after the threshold. Next, while accounting for the threshold effect at 40 d, we identified an age by population size interaction in which survival of yearling and adult CSTG changed across time. Yearlings exhibited substantially higher survival probabilities when the population at the release site was small (≤ 10 males on lek) during early translocation years, and adults exhibited substantially higher survival probabilities when the population at the release site was moderate or large (≥ 8 males on lek) during latter years of the translocation. This might represent inverse density dependent effects on survival wherein adult survival improved concomitantly with increases in population sizes. Short-term, post-release survival is less intuitive for yearlings, but yearlings greatly outperformed adults during the critical first three years of the reintroduction (i.e., the establishment phase) when the population at the release site was very small. In future reintroduction projects, establishing a population with translocated yearling CSTG followed by adults might hasten conservation goals.
