Molt Cycle of the Red-Backed Sandpiper (Calidris alpina) in Western North America

Holmes, Richard

The pterylogrpahy, molts, molt schedule, and criteria for age determination of Calidris alpina along the west coast of North America are described. The relationships of molt with breeding and with migration are discussed for this species, which nests at arctic latitudes and winters in north-temperate regions. In breeding populations of C. alpina in northern Alaska (71° N), the prebasic molt of adults is condensed into the short span of the arctic summer and overlaps with almost the whole of the breeding season. Molt begins early in the summer, and new flight feathers are completely grown before departure for winter quarters. At lower-latitude breeding localities in western Alaska (60-66° N), molt apparently starts later and breeding begins earlier than at the higher latitudes, with the result that less overlap occurs. Even in the northern populations, however, the major portion of energy expenditure on molt comes in late summer when breeding is over and young Red-backs are fully grown. Molt takes place during slow phases of both fall and spring migrations, energy reserves evidently being sufficient to support both activities. In periods of rapid migration, molt is suspended. The specializations in the molt schedule of C. alpina relate to the fact that this species, with its winter quarters in north-temperate regions, remains in the arctic through the end of summer, during which time it exploits tundra food sources in the absence of possible competitors.

Molt Cycle of the Red-Backed Sandpiper (Calidris alpina) in Western North America

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