Evaluating staging habitat quality to advance the conservation of a declining migratory shorebird, Red Knot Calidris canutus

Identifying where and when population “bottlenecks” occur is critical to the conservation of migratory species, many of which are declining precipitously worldwide. Especially challenging is the evaluation of changes to staging sites. These sites are indispensable links in the migratory cycle but are typically used only briefly.

We devised a field-based approach to assess the quality and carrying capacity of a critical staging site in Nanpu, China, for the declining, migratory Red Knot (Calidris canutus rogersi & C. c. piersmai) during northward migration. The Nanpu tidal flat supports 50,000-100,000 Red Knots annually, and while there, the knots feed almost exclusively on the bivalve Potamocorbula laevis. We simultaneously monitored changes in the abundance of Red Knots and bivalves across the entire staging site in spring 2018.

After taking into account potential competition with other shorebird species, we estimated that the Nanpu tidal flat was capable of supporting approximately 1.46-1.70 times the current observed level of usage of the site by Red Knots, and therefore is operating below, but close, to carrying capacity with respect to food resources for Red Knots. This result suggests that any further development of this site could harm the EAAF Red Knot population.

Synthesis and applications: Quantitative monitoring and evaluation of habitat quality of staging sites are essential to successfully conserve declining migratory species. In particular, researchers and conservation practitioners should incorporate both population size and staging duration in order to more accurately assess the importance of different sites and to quantify how changes in staging habitat quality may translate into changes in migrant population sizes at both local and global scales.

明确种群瓶颈（population bottlenecks）发生的时间与地点，对于迁徙物种的保护至关重要——全球范围内众多迁徙物种正急剧衰退。而中途停歇地（staging sites）的变化评估尤具挑战性：此类生境是迁徙周期中不可或缺的关键环节，但物种通常仅在此短暂停留。
本研究针对正在衰退的迁徙性红腹滨鹬（Red Knot，*Calidris canutus rogersi* 与 *C. c. piersmai*）北上迁徙过程中的关键中途停歇地——中国南堡潮间带，开发了一套野外实地研究方法，以评估其生境质量与环境容纳量（carrying capacity）。南堡潮间带每年可支撑5万至10万只红腹滨鹬在此栖息，期间这些鸟类几乎完全以光滑河篮蛤（*Potamocorbula laevis*）为食。2018年春季，研究团队同步监测了整个中途停歇地内红腹滨鹬与双壳类动物的丰度变化。
在考虑了与其他滨鸟（shorebird species）的潜在种间竞争后，研究团队估算得出：南堡潮间带的承载能力约为当前红腹滨鹬实际使用量的1.46至1.70倍，即该生境的食物资源供给水平略低于但接近红腹滨鹬的环境容纳量。这一结果表明，若对该停歇地进行进一步开发，将可能损害东亚-澳大利西亚迁飞区（East Asian-Australasian Flyway, EAAF）内的红腹滨鹬种群。
综合与应用：针对中途停歇地生境质量开展定量监测与评估，是成功保护衰退型迁徙物种的核心前提。尤为重要的是，研究人员与保护从业者应同时纳入种群规模与停歇时长两个指标，以便更精准地评估不同停歇地的重要性，并量化中途停歇地生境质量变化如何在局地与全球尺度上影响迁徙种群的规模变化。