BRANTA — Chi-Yeung Choi
Ecological research on Dunlin (Calidris alpina) at Chongming Dongtan, China
Institution: Fudan University, China
Supervisors: Prof Zhijun Ma
School of Biological Sciences,
The University of Queensland,
Subject Keywords:Chongming Dongtan, Dunlin, migratory stopover, wintering ecology, age determination, energetic condition
Species Keywords: Dunlin
The Dunlin (Calidris alpina) is a small-sized migratory bird species belonging to the order Charadriiformes, Family Scolopacidae and Genus Calidris. It is one of the most common shorebird species along the East Asian-Australasian Flyway (hereafter EAAF). Ten subspecies have been identified globally, and at least 4 of them occur along the EAAF. Chongming Dongtan (hereafter CMDT) is located at the Yangtse River estuary and in the middle of the EAAF. CMDT also plays an important role as a stopover and wintering site for migratory birds. The number of Dunlin found in CMDT exceeds 1% of the total Dunlin population along the EAAF and therefore, CMDT is of significance for Dunlin conservation, providing an ideal site for research on the stopover ecology and wintering ecology of this species.
The present study first describes age-determination of Dunlin along the EAAF and evaluates the reliability of different plumage characters in indicating age. After that, the age-related variations in migration timing, energetic condition and moult are investigated. Finally, the difference in energetic condition between Dunlin and other calidrid sandpipers (Great Knot (Calidris tenuirostris), Red Knot (Calidris canutus), Red-necked Stint (Calidris ruficollis) and Long-toed Stint (Calidris subminuta)) between different seasons are compared with the aim of understanding the relationship between migration strategies and energetic states, as well as fuel deposition. The main conclusions were as follows:
1. An effective age determination method was developed after comparison between Dunlin samples from breeding grounds in Alaska and several wintering grounds in mainland China and Taiwan. The pattern of white on the tip of primary coverts proved to be an important ageing criterion for Dunlin along the EAAF. About 90% of first-year Dunlin had a symmetrical white tip on their primary coverts, while the white tip of 73%-89% of adult Dunlin was either step-like or droplet-like. In addition, most first-year Dunlin had a continuous buff edge to their median coverts, and some tertials or tertial coverts were marked with a dark sub-terminal band. The usefulness of different ageing criteria varies with location and season, this especially being the case for the “adult buff ” coverts, which present only in some subspecies. Due to limiting factors such as moult, feather abrasion and bleach of colors, a combination of several available plumage characters provides the best basis for ageing Dunlin along the EAAF.
2. Based on a comparison of migration time and energetic condition between different periods and different age-groups of Dunlin, the body weight and energetic state of Dunlin were the lowest after southward migration. These remain stable throughout the winter period and reaching peaks before northward migration. In addition, the energetic state of first-year Dunlin was significantly lower than that of adults just before northward migration (May) and after southward migration (September and October). It should be noted that more than half of the early-returning adults are second-year birds, many of them may be failed breeders or not performing a complete migration. The general age structure of Dunlin in CMDT during migration and wintering period were dominated by first-year birds. Adding the state of body moult to the consideration, Dunlin in active moult had a significantly higher energetic state than those which had not started or suspended their body moult, and again those with completed body moult tended to have a higher energetic state. These findings indicate that body moult does have an impact on the condition index and the fuel deposition. The comparison between arrival time of different age-groups in Europe, America and CMDT during southward migration suggested that there is a close link between the timing of primary moult and the arrival sequence to wintering grounds. Among the subspecies that moult their primaries in breeding grounds, the first-year Dunlin arrived simultaneously with adults or sometimes even earlier than them. Among those with primary moult during southward migration stopover or after southward migration, the adults arrived at stopover sites and wintering grounds before first-year birds.
3. Comparison of body condition and fuel deposition patterns in Dunlin and four other calidrid sandpipers at CMDT indicated that the body condition and fuel deposition patterns within each species varied between seasons and between age-groups. In addition, the body condition and fuel deposition patterns differed among species that employ different migration strategies. Dunlins that winter at CMDT and in nearby areas, showed a significantly higher body condition during northward than southward migration stopover, most likely in anticipation of the longer travelling distance after leaving CMDT in spring. In contrast, Great Knots Calidris tenuirostris and Red Knots Calidris canutus perform a long-distance nonstop flight from CMDT to northwest Australia in boreal autumn, while covering a relatively short distance between CMDT and the north Yellow Sea region in boreal spring. As a consequence both species attained a significantly higher body condition at CMDT during the southward than northward migration. Moreover, they showed a significant increase in body condition at CMDT during the northward migration stopover, which we interpret as a recovery from the long flight from Australia. Red-necked Stints Calidris ruficollis and Long-toed Stints Calidris subminuta on the other hand, employing series of relatively short-distance flights during migration, showed no significant difference in departure body condition at CMDT between seasons, nor any significant increase in body condition in adults during either migration stopover. On the other hand, the first-year birds in all these five species showed a significant increase in body condition during the southward migration stopover, indicating the significant role of CMDT in the fuel deposition of first-year sandpipers. When considering the value of a particular stopover site for any species, the emphasis should not be exclusively on abundance; the role played by the site for different age-groups and in different seasons is of importance as well.
Choi, C.Y., Gan, X.J., Hua, N., Wang, Y., & Ma, Z.J. 2014. The habitat use and home range analysis of Dunlin (Calidris alpina) in Chongming Dongtan, China and their conservation implications. Wetlands, 34: 255-266.
Choi ,C.Y., Hua, N., Gan, X.J., Persson, C., Ma, Q., Zang, H.X., & Ma, Z.J. 2011. Age structure and age-related differences in molt status and fuel deposition of Dunlins during the nonbreeding season at Chongming Dongtan in east China. Journal of Field Ornithology, 82(2): 202-214.
Choi, C.Y., Hua, N., Persson, C., Chiang, C.Y., & Ma, Z.J. 2010. Age-related plumage differences of Dunlins along the East Asian-Australasian Flyway. Journal of Field Ornithology, 81(1): 99-111.
Choi, C.Y., Gan, X.J., Ma, Q., Zhang, K.J., Chen, J.K., & Ma, Z.J. 2009. Body condition and fuel deposition patterns of calidrid sandpipers during migratory stopover. Ardea, 97(1): 61-70.