RESIDENCY PATTERNS OF MIGRATING SANDPIPERS AT A MIDCONTINENTAL STOPOVER

Arctic-nesting shorebirds require several refueling stops during their long migrations between breeding grounds and Central and South Americ an wintering areas. The protection of stopover habitats for transconti nental migrants depends on whether birds fly long distances between a few select sites or fly short distances and stop at several wetlands. Although the Great Plains historically provided a vast array ofwetland s for use by migrants, wetland loss and conversion have reduced the av ailability of stopover sites in recent decades. In this study, we exam ined (1) residency periods, (2) fat dynamics, and (3) migration chrono logy of two shorebird species, the Semipalmated Sandpiper (Calidris pu silla) and White-rumped Sandpiper (C. fuscicollis) at Quivira National Wildlife Refuge (NWR), Kansas. Semipalmated Sandpipers had prolonged periods of species residency with overlapping arrivals and departures. Individual residency periods were highly variable and were unrelated to lipid reserves upon arrival. In contrast, White-rumped Sandpipers a rrived and departed more synchronously. Birds that arrived in poor con dition stayed longer than those with more body fat in 1991, but not in 1992. Wind direction did not influence patterns of departures of eith er species. We hypothesize that Semipalmated Sandpipers are ecological ly eurytopic when migrating across the Great Plains in the spring. Hig hly variable patterns in arrival, residency, and lipid levels indicate that spring migration of this species is relaxed and opportunistic. W hite-rumped Sandpipers showed a pattern of reduced flexibility. Flight range estimates suggest that most birds require intermediate stopover s before reaching the breeding grounds. Interior wetlands appear to fu nction as migration stopovers rather than staging areas for shorebirds .