Evaluate and simulate the reproduction and survival of a reintroduced population in an endangered bird species Crested ibis (Nipponia nippon)

Abstract

O_LIReintroduction programs are critical for restoring endangered species. However, scientific assessments and management recommendations based on comprehensive vital rates across the entire life cycle remain limited for such programs. The Crested ibis (Nipponia nippon), once nearly extinct, has been the focus of intensive conservation efforts, including reintroduction into its historical range. Here, we systematically evaluate the success of a Crested ibis reintroduction population by integrating long-term field monitoring with population dynamic modeling. C_LIO_LIWe conducted a systematic, multi-year (2023-2025) demographic study of a reintroduced Crested ibis population in Dongzhai National Nature Reserve, China. From 2013 to 2023, a total of 133 captive Crested ibises were released in seven batches within the nature reserve. By 2025, the wild population had exceeded 500. Based on the combination of field monitoring (n = 176 pairs) and GPS telemetry (n = 74 GPS tags, the longest monitoring time lasting 4 years), we quantified reproductive output and mortality rates across six life stages: nest building, incubation, offspring provisioning, fledgling (< 1 year), sub-adult (1-2 years), and adult (> 2 years). C_LIO_LIThe results show that the average clutch size of this population is 3.24 {+/-} 0.08, and each pair of parent birds can rear 1.31 {+/-} 0.12 nestlings to fledging each year. We found that high mortality during the incubation (32.5%, n = 425 eggs), offspring provisioning (34.1%, n = 287 chicks), and fledgling stages (38.6%, n = 63 birds). Key causes included unfertilized eggs, predation, starvation, and human disturbance. On the other hand, the mortalities in the nest building (9.1%, n = 176 pairs), sub-adult (9.8%, n = 28 birds) and adult stage (21.3%, n = 15 birds) were relatively low. Stage-structured matrix model shows a positive population growth of this reintroduced population (growth rate {lambda} = 1.053), with the population expected to increase 13-fold over 50 years (6,858 individuals). Sensitivity analysis indicates that adult survival had the strongest influence on population growth. Correspondingly, we predict that by 2075, its distribution range will expand 13-fold in tandem with population growth, exceeding 51,000 km{superscript 2} and covering several surrounding cities. C_LIO_LIOur comprehensive monitoring, evaluation, and simulation across the full life-cycle confirm that the reintroduced population is successfully established and self-sustaining. This finding addresses a critical research gap: the lack of a scientific and systematic framework for assessing population reintroductions in endangered species. Furthermore, we identified key conservation practices to enhance population growth and stability, including predator control, supplemental feeding, the rescue of weak chicks, and reducing human disturbance through public engagement. To ensure long-term viability, we also recommend implementing genetic management to avoid inbreeding. The resulting framework provides a practical model for improving reintroduction success and promoting species recovery in other endangered species. C_LI