Differentiating between stopover and staging sites: functions of the southern and northern Yellow Sea for long‐distance migratory shorebirds

Abstract

Evidence‐based protection of migratory birds at flyway levels requires a solid understanding of their use of ‘stopping sites’ during migration. To characterize the site use of northward‐migration great knots Calidris tenuirostris in China, we compared length of stay and fuel deposition during northward migration at areas in the south and the north of the Yellow Sea, a region critical for migrating shorebirds. Radio‐tracking showed that at the southern site great knots stayed for only short periods (2.3 ± 1.9 d, n = 40), and bird captures showed that they did not increase their mean body mass while there. In the north birds stayed for 1 month (31.0 ± 13.6 d, n = 22) and almost doubled their mean body mass. Fuel consumption models suggest that great knots departing from the northern Yellow Sea should be able to fly nonstop to the breeding grounds, whereas those from the south would require a refueling stop further north. These results indicate that the study sites in the northern and southern Yellow Sea serve different roles: the southern site acts as a temporary stopover area that enables birds with low fuel stores to make it to main staging areas further north, while the northern site serves as the critical staging site where birds refuel for the next leg of their migration. The rapid turnover rate in the southern Yellow Sea indicates that many more birds use that area than are indicated by peak counts. Differential use of the southern and northern sites indicates that both play crucial roles in the ability of great knots to migrate successfully.

Springtime migratory restlessness and departure orientation of Great Knots (Calidris tenuirostris) in the south compared to the north Yellow Sea

“…There are large areas of suitable habitats for Great Knots between the south and the north Yellow Sea but few between the north Yellow Sea and the breeding sites. Individuals of Great Knots remain in the south Yellow Sea for only a short period (average 2 days) and store little fuel before moving to the north Yellow Sea (Ma et al 2013;Peng et al 2015). Individuals in the north Yellow Sea, in contrast, stay for about 1 month on average and deposit sufficient fuel reserves for the much longer non-stop flight to the breeding sites (Ma et al 2013;Peng et al 2015).…”

“…1) is the first major stopover site for some Great Knots after a trans-Pacific flight of over 5000 km initiating from the nonbreeding sites (Battley et al 2000;Lisovski et al 2016). The coast along the Yalu Jiang estuary in the north Yellow Sea is one of the last refuelling sites before the final non-stop flight of over 4000 km to the breeding sites (Bamford et al 2008;Ma et al 2013;Lisovski et al 2016). There are large areas of suitable habitats for Great Knots between the south and the north Yellow Sea but few between the north Yellow Sea and the breeding sites.…”

“…The Great Knot is a mediumsized shorebird that performs long-distance migratory flights between their major nonbreeding sites in Northwest Australia and breeding sites in East Siberia. During northward migration, the presence of the Great Knot population in the Yellow Sea region lasts for nearly 2 months, where they refuel before flying to the breeding area (Ma et al 2013;Bai et al 2015). The Yangtze estuary in the south Yellow Sea (Fig.…”

“…Individuals of Great Knots remain in the south Yellow Sea for only a short period (average 2 days) and store little fuel before moving to the north Yellow Sea (Ma et al 2013;Peng et al 2015). Individuals in the north Yellow Sea, in contrast, stay for about 1 month on average and deposit sufficient fuel reserves for the much longer non-stop flight to the breeding sites (Ma et al 2013;Peng et al 2015). Departures of Great Knots in the south Yellow Sea extend over a long time period, and the departure date is unsynchronized among individuals but is related to wind conditions (Ma et al 2011).…”

Threats to migratory birds, and actions for their conservation

“…This is partly because great knots prefer to fly shorter distances than bar-tailed godwits (Fig. 5.1) and are dependent on stopover sites to complete both their northward and southward migration (Yang et al, 2011;Ma et al, 2013;Choi et al, 2015).…”