Factors affecting post-release survival and dispersal of reintroduced Crested Ibis(Nipponia nippon) in Tongchuan City, China

Reintroduction has become a common conservation management tool to restore endangered species in their historical range. However, many attempts have failed to establish self-sustaining populations in the wild. The success of reintroductions could be improved by varying release strategies. Therefore, it is vital to determine the factors influencing reintroduction outcomes. To better understand the post-release settlement and to optimize the release strategy of the Crested Ibis(Nipponia nippon), we quantified the effects of age, sex, acclimation duration,and the timing of release events on post-release survival and dispersal distance for the released Crested Ibis in Tongchuan City, Shaanxi Province, using a generalized linear mixed effect modeling approach. Our results indicate that 40–56.3% of the released individuals survived the first year following release. Mortality was attributable to flight collisions, starvation, disease, and unknown reasons. The post-release survival probability of ibises showed a negative association with age(estimate=-0.186; 95% CI:-0.350 to-0.022; P=0.026), and post-release dispersal distance was affected by the timing of release event(estimate=0.718; 95% CI: 0.025 to1.253; P=0.042). However, sex and acclimation period duration did not cause detectable differences in postrelease survival probability and dispersal distance. Based on our results, optimal release strategies for establishing a reintroduced population of the Crested Ibis include:(1) release of sub-adults biased and sex ratio balanced initial groups;(2) release during the non-breeding season; and(3) food supplementation immediately after release.