Differential migration in birds creates skewed latitudinal wintering distributions of sex and age classes. Both endogenous and exogenous factors influence migration patterns, although the relative effects vary greatly between species, and among individuals within a species. A strong endogenous component may control migratory features such as migration distance, direction and timing. This project intends to examine the roles of endogenous and exogenous factors in settlement patterns of juvenile female and male Western Sandpipers (Calidris mauri). The expression of Zugunruhe (migratory restlessness) and orientation in juveniles of different sex will be measured. The effects of restricted food resources and social status on the expression of Zugunruhe in juveniles before and after the termination of migration will be examined. The behavior of short-stopped, free-living juveniles to compare the ability of the sexes to live in the northern part of the species winter range, and area where females do not typically settle will be monitored. This study will contribute to the understanding of the evolution of differential migration, as it incorporates analysis of both heritable and ecological factors in explaining the distribution of sex classes during the nonbreeding season.
