Summary: Reintroduction projects usually attempt to re-establish a self-sustaining population of endangered species within their historical ranges through the release of captive-bred individuals into the wild. We studied the breeding biology and nesting success of a reintroduced population of Crested Ibis Nipponia nippon in Ningshan County on the south slope of the Qinling Mountains of Shaannxi Province, China. From May 2007 to October 2011, 56 captive-bred individuals, composed of 26 females and 30 males, were released into the area and monitored using radio-telemetry. The average age of individuals at release was 5.2 ± 2.5 years for females and 6.4 ± 2.9 years for males. Mean clutch size was 3.14±1.06 (range 1-5). Mean number of fledglings per active nest was 1.57 ± 1.03 and mean number of fledglings per successful nest was 2.00 ± 0.87. Most of the fledglings survived to complete their post-fledging dispersal. Mean annual survival rate was 0.552 ± 0.064 for all released birds, 0.815 ± 0.054 for breeders, and 0.515 ± 0.058 for first year fledglings. The average number of young produced/year/pair was 1.57 ± 1.03 and the growth rate (λ) of the reintroduced population was 1.2193. We confirmed that starvation and predation by King Rat Snake Elaphe carinata were the main causes of death of released individuals, nestlings and fledglings. This is the first attempt to reintroduce captive-bred Crested Ibis to former natural habitat. The ability of captive-bred ibis to survive and breed successfully bodes well for future releases of this and other endangered species.

Bird sex chromosomes play a unique role in sex-determination, and affect the sexual morphology and behavior of bird species. Core waterbirds, a major clade of birds, share the common characteristics of being sexually monomorphic and having lower levels of inter-sexual conflict, yet their sex chromosome evolution remains poorly understood. Here, by we analyse of a chromosome-level assembly of a female crested ibis (Nipponia nippon), a typical core waterbird. We identify neo-sex chromosomes resulting from fusion of microchromosomes with ancient sex chromosomes. These fusion events likely occurred following the divergence of Threskiornithidae and Ardeidae. The neo-W chromosome of the crested ibis exhibits the characteristics of slow degradation, which is reflected in its retention of abundant gametologous genes. Neo-W chromosome genes display an apparent ovary-biased gene expression, which is largely driven by genes that are retained on the crested ibis W chromosome but lost in other bird species. These results provide new insights into the evolutionary history and expression patterns for the sex chromosomes of bird species.

Background: 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.Methods: 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.Results: 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.Conclusions: 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.

Summary: A reintroduction project for the endangered Crested IbisNipponia nipponwas conducted in Ningshan County (Shaanxi Province) on May 31, 2007. Post-release monitoring of the survival of the reintroduced population was carried out extensively from 2008 to 2015. Data collected over eight years after release were used to estimate the annual survival rate for different cohorts using a Cormack-Jolly-Seber model with capture-recapture data. The mean annual survival rates for all individuals were estimated to be 0.738 (95% CI: 0.547–0.801) and 0.752 (95% CI: 0.478–0.887) for released birds. For different age classes in the recipient population, the survival rates were estimated to be 0.384 (95% CI: 0.277–0.504), 0.853 (95% CI: 0.406–0.978), and 0.812 (95% CI: 0.389–0.950) for yearlings, juveniles and adults, respectively. The higher mortality for yearlings has greatly decreased the survival rate and our focal population was indeed sensitive to changes in yearling survival. Therefore, effective protection of yearlings was crucial to population persistence, as well as to juveniles and adults. The large proportion of mature individuals in our focal population indicated a gradually growing population. There was a slight bias towards males in the adult sex ratio with the increase of wild-born offspring, but it was not statistically significant. Therefore, we conclude that the primary goal of establishing a self-sustaining population of the Crested Ibis in part of their historical range has been achieved. Finally, we discuss factors affecting the survival of the reintroduced population and we propose some changes for future management of endangered species.