Offspring of translocated individuals drive the successful reintroduction of Columbian Sharp-tailed Grouse in Nevada, USA

Abstract

Translocations of North American prairie-grouse (genus Tympanuchus) present a conservation paradox wherein they are performed to augment, restore, or reintroduce populations, but translocated individuals exhibit a diminished ability to contribute to population restoration. For reintroduced populations without immigration, persistence can only be achieved through reproductive contributions by translocated individuals and their progeny. Due to the disruptive nature of translocation (e.g., physiological chronic stress), progeny produced at restoration sites may outperform founder populations in terms of demographics, but this hypothesis has yet to be tested. We reintroduced Columbian Sharp-tailed Grouse (T. phasianellus columbianus; CSTG) to north central Nevada from 2013 to 2017 and used integrated population models (IPMs) to evaluate the process of population establishment and estimate latent contributions of progeny hatched at the restoration site to population rate of change (λ). Specifically, we used annual lek (i.e. communal breeding arenas) counts and demographic data from translocated individuals to build two separate IPMs to estimate λ. While keeping demographic contributions by translocated individuals identical between models, one IPM assumed local progeny performance was demographically similar to translocated individuals (i.e. the baseline-IPM), and the second assumed that local progeny performed demographically similar to non-translocated CSTG (i.e. the informative-IPM). The baseline-IPM predicted strong population declines following the conclusion of translocations and extirpation by 2020, and it failed to predict observed lek counts. Conversely, the informative-IPM predicted population growth rates (λ = 1.17, 95% credible interval [CI]: 0.74-1.50) that were more similar to field observations. Offspring of translocated individuals likely perform at similar levels to non-translocated populations, and by not accounting for demographic differences between translocated individuals and non-translocated progeny hatched at the restoration site, managers could underestimate population performance and persistence. Thus, translocation practices that maximize the number of offspring immediately recruited into restoration sites are likely to be the most successful.