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 to 1.253; P = 0.042). However, sex and acclimation period duration did not cause detectable differences in post-release 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.
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Open Access
Research
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One of the most challenging tasks in wildlife conservation and management is clarifying which and how external and intrinsic factors influence wildlife demography and long-term viability. The wild population of the Crested Ibis (Nipponia nippon) has recovered to approximately 4400, and several reintroduction programs have been carried out in China, Japan and Korea. Population viability analysis on this endangered species has been limited to the wild population, showing that the long-term population growth is restricted by the carrying capacity and inbreeding. However, gaps in knowledge of the viability of the reintroduced population and its drivers in the release environment impede the identification of the most effective population-level priorities for aiding in species recovery.
The field monitoring data were collected from a reintroduced Crested Ibis population in Ningshan, China from 2007 to 2018. An individual-based VORTEX model (Version 10.3.5.0) was used to predict the future viability of the reintroduced population by incorporating adaptive patterns of ibis movement in relation to catastrophe frequency, mortality and sex ratio.
The reintroduced population in Ningshan County is unlikely to go extinct in the next 50 years. The population size was estimated to be 367, and the population genetic diversity was estimated to be 0.97. Sensitivity analysis showed that population size and extinction probability were dependent on the carrying capacity and sex ratio. The carrying capacity is the main factor accounting for the population size and genetic diversity, while the sex ratio is the primary factor responsible for the population growth trend.
A viable population of the Crested Ibis can be established according to population viability analysis. Based on our results, conservation management should prioritize a balanced sex ratio, high-quality habitat and low mortality.
