THE MIGRATION PATTERNS OF THE PURPLE SANDPIPER CALIDRIS-MARITIMA

The Purple Sandpiper breeds largely in the Arctic, and winters (boreal season) on the rocky shores of the north Atlantic, further north than any other sandpiper. As the populations from Canada, Greenland, Iceland, Svalbard, Norway and Russia differ in wing and bill lengths it is possible to match measurements taken from breeding birds with samples of birds caught in winter. Ringing recoveries, especially from colour marked birds, have also helped to determine migration routes and wintering areas. Four populations move to the nearest ice-free coast. Two populations move south of the nearest ice-free coast, being replaced by larger birds from a more northerly population (''chain migration''). Only the north Canadian population is believed to migrate a long distance, ''leap-frogging'' other winter populations. These patterns are discussed in relation to theories for the migration patterns of waders.