Dietary divergence and temporal partitioning facilitate the stopover coexistence of two molluscivorous shorebird species in the Yellow Sea

Species coexistence, largely maintained through mechanisms of niche differentiation, is fundamental for sustaining biodiversity and ecosystem resilience. For migratory shorebirds, the limited availability of staging sites intensifies interspecific competition, making coexistence mechanisms critical for refueling and survival during migration. This study examined the coexistence mechanisms of two threatened shorebird species, the Great Knot ( Calidris tenuirostris ) and Red Knot ( Calidris canutus ), in Nanpu wetland, a key stopover site along the East Asian Australasian Flyway. Using noninvasive DNA metabarcoding of 81 droppings, we identified 32 MOTUs, revealing that both species primarily feed on Bivalvia. The Great Knot exhibited a more diverse diet, with Mactra quadrangularis (FOO = 71.43%, RRA = 69.41%) as its primary food source, whereas the Red Knot specializes in feeding on Potamocorbula laevis (FOO = 93.48%, RRA = 80.15%). Long-term survey data collected from 2014 to 2024 revealed that the abundance of Great Knots peaked in late April, whereas the number of Red Knots peaked 12.6 days later, in mid-May. These findings highlight how dietary differentiation and temporal partitioning enable the coexistence of these threatened species, offering valuable insights for the development of targeted conservation strategies to support species with specialized diets in adapting to fluctuations in food resources.