Ecological Factors Influencing the Breeding Season Schedule of Western Sandpipers (Calidris mauri) in Subarctic Alaska

Abstract

Studies of the breeding system ecology of the Western Sandpiper (Calidris mauri) were conducted in the summers of 19661969 on the Yukon-Kuskokwim Delta in western Alaska. Western Sandpipers arrive as soon as the snow begins to melt, establish territories on heath tundra, pair and nest once. Second nestings are restricted to replacement clutches. As soon as breeding is completed, the adults shift to coastal habitats, begin molt, and by early to mid-July move S on migration. Young mauri follow about 2 to 3 weeks later. After their arrival on Pacific coast feeding areas, the adults continue their prebasic molt, completing it by late October. The single nesting and early departure of Western Sandpipers from the breeding areas are related to a decreasing food supply in an otherwise favorable environment. The only other congener sympatric with mauri on the Delta, C. alfpina, follows an identical breeding schedule, but remains longer in the N, occupying riverbank and intertidal habitats, and completes its molt before migrating S in late September. This extended residence of alpina in Alaska is possible because it is able to exploit marine invertebrates there during late summer, whereas mauri apparently is not. Therefore, the changes in food abundance near the nesting areas and the lack of suitable food supply in midsummer are the primary factors influencing the scheduling of breeding season events in Western Sandpiper populations.