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Many migratory birds exhibit interannual consistency in migration schedules, routes and stopover sites. Detecting the interannual consistency in spatiotemporal characteristics helps understand the maintenance of migration and enables the implementation of targeted conservation measures. We tracked the migration of Whimbrel (Numenius phaeopus) in the East Asian–Australasian Flyway and collected spatiotemporal data from individuals that were tracked for at least two years. Wilcoxon non-parametric tests were used to compare the interannual variations in the dates of departure from and arrival at breeding/nonbreeding sites, and the interannual variation in the longitudes when the same individual across the same latitudes. Whimbrels exhibited a high degree of consistency in the use of breeding, nonbreeding, and stopover sites between years. The variation of arrival dates at nonbreeding sites was significantly larger than that of the departure dates from nonbreeding and breeding sites. Repeatedly used stopover sites by the same individuals in multiple years were concentrated in the Yellow Sea coast during northward migration, but were more widespread during southward migration. The stopover duration at repeatedly used sites was significantly longer than that at sites used only once. When flying across the Yellow Sea, Whimbrels breeding in Sakha (Yakutia) exhibited the highest consistency in migration routes in both autumn and spring. Moreover, the consistency in migration routes of Yakutia breeding birds was generally higher than that of birds breeding in Chukotka. Our results suggest that the northward migration schedule of the Whimbrels is mainly controlled by endogenous factors, while the southward migration schedule is less affected by endogenous factors. The repeated use of stopover sites in the Yellow Sea coast suggests this region is important for the migration of Whimbrel, and thus has high conservation value.

Abstract Background Conserving migratory birds is challenging due to their reliance on multiple distant sites at different stages of their annual life cycle. The concept of “flyway”, which refers to all areas covered by the breeding, nonbreeding, and migrating of birds, provides a framework for international cooperation for conservation. In the same flyway, however, the migratory activities of the same species can differ substantially between seasons and populations. Clarifying the seasonal and population differences in migration is helpful for understanding migration ecology and for identifying conservation gaps. Methods Using satellite-tracking we tracked the migration of Whimbrels (Numenius phaeopus variegatus) from nonbreeding sites at Moreton Bay (MB) and Roebuck Bay (RB) in Australia in the East Asian–Australasian Flyway. Mantel tests were used to analyze the strength of migration connectivity between the nonbreeding and breeding sites of MB and RB populations. Welch’s t test was used to compare the migration activities between the two populations and between northward and southward migration. Results During northward migration, migration distance and duration were longer for the MB population than for the RB population. The distance and duration of the first leg flight during northward migration were longer for the MB population than for the RB population, suggesting that MB individuals deposited more fuel before departing from nonbreeding sites to support their longer nonstop flight. The RB population exhibited weaker migration connectivity (breeding sites dispersing over a range of 60 longitudes) than the MB population (breeding sites concentrating in a range of 5 longitudes in Far Eastern Russia). Compared with MB population, RB population was more dependent on the stopover sites in the Yellow Sea and the coastal regions in China, where tidal habitat has suffered dramatic loss. However, RB population increased while MB population decreased over the past decades, suggesting that loss of tidal habitat at stopover sites had less impact on the Whimbrel populations, which can use diverse habitat types. Different trends between the populations might be due to the different degrees of hunting pressure in their breeding grounds. Conclusions This study highlights that conservation measures can be improved by understanding the full annual life cycle of movements of multiple populations of Whimbrels and probably other migratory birds.

Determining the migration routes and connections of migratory birds at the population level helps clarify intraspecific differences in migration. Five subspecies have been recognized in the Whimbrel (Numenius phaeopus) in Eurasia. Ssp. rogachevae is the most recently described subspecies. It breeds in Central Siberia, while its non-breeding region and migration routes are still unclear. We tracked the migration of Eurasian Whimbrels captured at three non-breeding sites (Moreton Bay in east coast of Australia, Roebuck Bay in Northwest Australia and Sungei Buloh Wetland in Singapore) and two migration stopover sites (Chongming Dongtan and Mai Po Wetland in China). We determined the breeding sites and inferred the subspecies of the tagged birds in the East Asian – Australasian Flyway (EAAF) based on the known breeding distribution of each subspecies. Of the 30 tagged birds, 6 and 21 birds bred in the breeding range of ssp. rogachevae and variegatus, respectively; one bred in the presumed transition area between the breeding range of ssp. phaeopus and rogachevae, and two bred in the region between the breeding range of ssp. rogachevae and variegatus. The birds that bred in the ssp. rogachevae breeding range spent their non-breeding season in the northern Sumatra, Singapore, East Java and Northwest Australia and mainly stopped over along China's coasts during migration. None of our birds bred in the exclusive breeding range of the phaeopus subspecies. Previous studies have predicted that rogachevae whimbrels migrate along the Central Asian Flyway and spend the non-breeding season in West India and East Africa. We found that at least some rogachevae whimbrels migrate along the EAAF and spend the non-breeding season in Southeast Asia and Australia. The ssp. phaeopus is at best sparsely distributed in the EAAF in the west region, or possibly does not occur at all.