Ecological barrier crossing strategies in longitudinal migrants: a case study of Mongolian gulls (Larus mongolicus) distributed in East Asia.

backgroundEcological barriers are major factors shaping the migratory strategies of birds. The Mongolian Plateau, with sparse and fragmented wetlands, provides limited stopover for waterbirds. Recent studies revealed that several bird species migrate longitudinally between their breeding sites in central Asia and the coasts of East Asia, thereby crossing the Mongolian Plateau. However, how these birds adapt their migratory strategies to cope with the environmental constraints imposed by the Mongolian Plateau remains poorly understood.

methodsTo address this gap, we focused on the Mongolian gull (Larus mongolicus), a representative longitudinal migrant that migrates along the East Asian coast and crosses the Mongolian Plateau. Using satellite tracking data from 29 coastal and 30 inland migration events in spring, and 34 coastal and 33 inland migration events in autumn between 2018 and 2025, we analyzed the difference in their migration duration, stopover duration, travel duration, migration distance, number of stopover sites, daily travel speed, straightness index and flight altitude relative to the ground between coastal and inland migration stage.

resultsWe found that, in both spring and autumn, inland migration across the Mongolian Plateau covered significantly longer distance than coastal migration and was associated with higher daily travel speed. Migration duration, stopover duration, and number of stopover sites were all markedly lower during inland migration than during coastal migration, particularly in autumn. Flight altitude relative to the ground was significantly higher during inland migration compared to coastal migration across both seasons. Furthermore, flight altitude relative to the ground exhibited a pronounced diel pattern across inland and coastal migration stage, with birds flying at lower altitudes at night, increasing altitude during the day, and decreasing altitude toward dusk.

conclusionsMongolian gulls adopt a strategy of rapidly crossing the Mongolian Plateau and adjacent arid and semiarid areas by minimizing stopover use, increasing daily travel speed, and flying at higher altitudes. These findings highlight the Mongolian Plateau as an important ecological barrier shaping migration behavior in this species and, together with growing evidence from other tracked and banded species migrating across this region, suggest its broader ecological and conservation significance.