La Tour du Valat

Institut de recherche pour la conservation des zones humides méditerranéennes

Titre :	The seasonal pattern of numbers, population structure and migration of Purple Sandpipers Calidris maritima in Orkney
Auteurs :	C. J. Corse, Auteur ; R. W. Summers, Auteur
Type de document :	Article
Dans :	Ringing & Migration (19(4) Nov., 1999)
Article en page(s) :	275-282
Résumé :	There are two populations of Purple Sandpipers in Orkney; 'long-billed' birds, which predominate, and 'short-billed' birds. They arrived mainly during October and November, and departed in April and May from sites on Mainland and South Ronaldsay. On Sanday, densities were as high in April as in winter, and peak numbers occurred in early May, suggesting that this island is used for pre-migratory fattening. The percentage of first-year birds on Mainland varied annually between 5.8% and 30.5%. The mean mass in winter was relatively stable, between 67 and 71g. A change in population structure in terms of sex ratio and the ratio of 'short-billed' to 'long-billed' birds in May suggested that the two populations or sexes have different migration strategies. Ringing recoveries showed that birds wintering on North Sea coasts migrate through Orkney in May, joining birds which were resident over the winter. Purple Sandpipers increased in mass during May to a mean peak of ca. 90g in mid-May. The accumulation of fat for migration is sufficient for 'short-billed' birds to fly to Norway and the 'long-billed' birds to fly to Iceland where they are thought to refuel for further migration to Canada.

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