FAT-CONTENT AND STOPOVER ECOLOGY OF SPRING MIGRANT SEMIPALMATED SANDPIPERS IN SOUTH-CAROLINA

Semipalmated Sandpipers (Calidris pusilla) stop at staging areas during migration to replenish fat reserves that fuel long distance flights. We hypothesize that if sandpipers are minimizing time spent en route between wintering areas and breeding grounds, a negative correlation should exist between fat content upon arrival at a staging area and length of stay. We examined the relationship between these two variables at a spring staging area in coastal South Carolina using simple and multiple regression models. Length of stay was independent of estimated fat content at capture after controlling for date in the season. Birds with sufficient energy reserves for long distance flights were as likely to remain on the study area as lean birds. Date in the season showed more influence on stopover time than estimated fat mass at capture. Stopover time decreased with later date, suggesting an increase in the speed of migration as the season progressed. These results show that date is a critical variable influencing Semipalmated Sandpiper migration stopover strategy. Migrants appear to shift their migration priorities with respect to fat stores and stopover time as the season progresses.