Abstract:

Objective: This study aimed to understand the reproductive traits and estimate the current population size of the endangered Crested Ibis (Nipponia nippon), so as to provide a scientific basis for the population status assessment and efficient conservation and management. Method: We investigated the nest sites of wild Crested Ibis in Yangxian and the surrounding area of Shaanxi Province and the environmental factors and reproductive parameters of each nest from March to June, 2019, and analyzed the nesting success and breeding productivity. Meanwhile, a simultaneous survey at the nocturnal roosts was conducted in September 2019, to investigate the population size and age structure. According to nest-site density, a fixed Kernel method in ArcView GIS 3.3 was used to estimate the distribution and area of three different nesting ranges, and Crosstabs and ANOVA in SPSS 22.0 were used to compare the differences of reproductive traits. Result: A total of 449 nest sites were recorded in 2019, which mainly distributed in Yangxian (66.8%) and Chenggu (29.0%). Based on Fixed Kernel estimation, the size of core nesting range and regular nesting range of Crested Ibis were 244.1 km² and 1 523.7 km², respectively, with the nesting density in core range of 0.73 nests·km^-2, which was much higher than that in regular range with 0.16 nests·km^-2. The nesting success rate averaged 66.4%, and it increased from core range, regular nest range to peripheral nest range, and the difference was significant among the three nesting ranges. The breeding productivity averaged 2.05, and it was significantly higher in peripheral nesting range than that in the other two nesting ranges. A total of 19 species of nesting trees were recorded, dominated by Pinus spp. (30.2%), Ulmus pumila (28.6%) and Populus davidiana (26.6%). There was no significant difference of nesting success among the three tree species, but the breeding productivity in Pinus spp. was significantly higher than that in the other two species. A total of 2 571 individuals were recorded in 38 nocturnal roosts, among which Yangxian and Chenggu counties accounted for 73.7% and 15.8% of the total roosts, respectively, and 73.0% and 23.4% of the total number of birds, respectively. The fledglings accounted for 11.6% of the total population. Conclusion: The wild population of Crested Ibis is increasing steadily, and the most of the nest sites and nocturnal roosts are still distributed in Yangxian and Chenggu. However, the population growth in the core nesting range may have been experiencing the suppression from the environment capacity, and consequently the population is accelerating its dispersal outside. The age structure of wild population is changing, which will have impact on the population growth rate. It is crucial to facilitate the habitat restoration in the core ranging and efficient management of peripheral population.

Key words: Crested Ibis, breeding productivity, nocturnal roost, simultaneous count, environment capacity