Waders Class Stopover For Migrant Male As Early As The Present Preliminary Study

Protandry refers the earlier arrival to breeding sites or reproductive stages of male animals relative to females on average. Many migrants express protandrous arrival timing during spring migration. Studies had been mainly concerned on sexual dimorphism species, however, sexual homomorphous species may show different patterns. Similarly, many avian migrants show differential distributions during non-breeding season, mainly on sexs, ages and body sizes.Waders are one of the most important groups of migrants. Millions of waders migrate from breeding areas in polar region and temperate zones to the tropical and Southern Hemisphere. Waders are the important groups for ecological, behavioural and evolutionary researches because of their widely distribution, massive number and similar morphologic characteristics. However, protandrous arrival timings of waders were poorly studied except Pied Avocet(Recurvirostra avosetta), Curlew Sandpiper (Calidris ferruginea), Western Sandpiper(Calidris mauri) and some sexual reversal species, e.g. Phalarope (Phalaropodidae) and Spotted Sandpiper (Actitis macularia).The East Asian-Australasian Shorebird Flyway, which links the breeding grounds in eastern Siberia with the non-breeding grounds in Australia and New Zealand, is used by more than five million migratory shorebirds annually. However, most of the former studies have been assembled in the Pacific-American Flyway and African-European Flyway, little is known about the occurrence of differential migration in the East Asian-Australasian Flyway. Former studies showed that differential migration happens in this flyway.In this thesis, I will first introduce six hypotheses to explain migrants' protandrous arriving, including rank advantage, susceptibility, constraint, mate opportunity, waiting cost and mate choice hypothesis, five hypotheses to explain differential migration of males and females, including dominance, body size, arrival time, predation risk and resource partitioning hypothesis, then we try to test the hypotheses of waders'arrival timing and wintering segregation in two parts as below:First, I collected feather samples and data of waders during 2008 spring migration in Chongming Dongtan and Hebei Tangshan, used genetic methods to sex the birds, including Great Knot(Calidris tenuirostris), Red Knot(Calidris canutus), Red-necked Stint(Calidris ruficollis), Dunlin(Calidris alpina), Sharp-tailed Sandpiper(Calidris acuminata), Terek Sandpiper (Xenus cinereus), Bar-tailed Godwit (Limosa lapponica) which stopped at Chongming Dongtan, and Red Knot, Red-necked Stint, Curlew Sandpiper (Calidris ferruginea), Sanderling (Calidris alba) which stopped at Hebei Tangshan. Then compared sex ratios with capture dates to find differential spring migration patterns between sexes.Second, in order to test constraint hypothesis in protandrous dunlin, I collected feather samples and data of dunlins wintering in Fujian Putian, Hunan Dongting Lake, Anhui Caizi Lake, Chongming Dongtan, Jiangsu Lianyungang and Hebei Tangshan during Dec.2007 to Mar.2008, used genetic methods to sex the samples. Then, I studied the differential distribution patterns of wintering dunlin, and discussed the relationship between wintering sexual segregation and protandrous arrival timing.The main conclusions were as below:1. Red Knot, Red-necked Stint, Sharp-tailed Sandpiper, Terek Sandpiper and Bar-tailed Godwit which stop at Chongming Dongtan show protandrous arrival timing, males arrive at Chongming Dongtan 9 days,9.5 days,10.5 days,5.5 days and 4 days earlier than females, male ratio decline significantly in Sharp-tailed Sandpiper and Terek Sandpiper. Protandry occure in Red Knot, Red-necked Stint, Curlew Sandpiper, Sanderling which stop at Hebei Tangshan, males arrive at Hebei Tangshan 2.5 days,5.5 days, 4 days,3.5 days earlier than females, male ratio decline significantly in Curlew Sandpiper and Sanderling.2. According to the "male ratio-date" analysis, combine with subspecies of Dunlin and Bar-tailed Godwit in China, we infer that Dunlin show protandrous arrival timing, and Bar-tailed Godwit show protogynous arrival timing within one subspecies. Thus, I conclude that protandry occurs in Red Knot, Red-necked Stint, Dunlin, Sharp-tailed Sandpiper, Terek Sandpiper, Curlew Sandpiper and Sanderling, whereas protogyny occurs in Great Knot and Bar-tailed Godwit.3. Sexual size dimorphism is not so obvious in waders than in passerines, but females are a bit larger than males in most species. And this pattern happens in Red Knot, Red-necked Stint, Dunlin, and Bar-tailed Godwit, which show prominent protandrous arrival timing. Thus susceptibility hypothesis cannot be the unanimous explanations of waders'sexual differential migration, only protandrous Sharp-tailed Sandpiper and protogynous Great Knot fit its hypothesis. 4. According to data of dunlins wintering in Fujian Putian, Hunan Dongting Lake, Anhui Caizi Lake, Chongming Dongtan, Jiangsu Lianyungang and Hebei Tangshan, we studied the relationship between latitude and wintering dunlins'sex ratio, body mass, bill length, body size including wing and tarsus length. Although not significant, we found sex ratio decline, bill length decline and body mass rise along with the rise of latitude, whereas wing length and tarsus length do not show apparent linear trend. Our results supported resource partitioning and body size hypothesis, and denied arrival timing and predation risk hypothesis. We infer resource partitioning hypothesis as the main explanation of dunlins'wintering segregation, which need further research.5. With dunlins wintering pattern, mating system, protandrous arrival timing, and other relative knowledge, I infer constraint hypothesis as the explanation of protandrou arrival timing of dunlin. As it is also suitable for Curlew Sandpiper and Bar-tailed Godwit, I infer constraint hypothesis may explain most waders' protandrous/protogynous arrival timing.