Flexible nest site selection of the endangered Oriental Storks (Ciconia boyciana): Trade-off from adaptive strategies

Nest site selection is a vital component of bird reproduction success, and an adaptive behavior conducted to decrease nest predation risk with avoiding external disturbances. Understanding patterns of nest site selection can provide insights into how species adapt to changes in their habitat and has important conservation implications. In this study, we used microhabitat variables and multi-scale data with a field survey of nest occurrence to determine nest site selection patterns and adaptive strategies of the breeding Oriental Storks (Ciconia boyciana) in different nest areas. Results demonstrate that the nest site microhabitat characteristics of the breeding Oriental Storks significantly differed among the three nesting areas, and nest height was higher in the middle and lower Yangtze River floodplain than in the Northeast China and Bohai Bay nest areas. The food resources and intensity of human disturbance had the greatest effects on the nest site selection of the breeding Oriental Storks. The intensity of human disturbance was positively correlated with the nest height of the breeding Oriental Storks in Bohai Bay and the middle and lower Yangtze River floodplain; however, nest height decreased with the abundance of food resources in the Northeast China nest area. Our findings indicate that the nest site selection patterns of Oriental Storks showed flexible adaptive strategies. In safer environments, nests were lower and closer to food resources, which allows parent storks to invest more in the nestlings. However, in areas where human activity was intense, nests were higher to ensure the safety of their offspring. Some measures that could be taken to improve the breeding habitat of Oriental Storks include increasing the percentage of wetland areas in nesting areas to enhance food resources availability and setting artificial nests at suitable heights in potential nesting grounds to encourage nesting. Finally, the establishment of soft barriers around the nesting areas could increase the safety of nests.