Migration is one of the most engaging phenomena of the animal world and one that is epitomized by birds. Migratory birds spend different parts of the annual cycle in geographically disparate places. The conditions and selective pressures during each period are likely to affect individual performance during subsequent periods. This simple fact presents us with considerable obstacles to understanding how agents of global change (i.e., climate, land use) will influence the ecology, evolution, and conservation of migratory birds. Such interseasonal effects are poorly understood within most avian migration systems, in large part because it has been difficult to follow individuals and specific populations year-round (i.e., migratory connectivity). In addition, for most species there exists an extreme research bias toward breeding over nonbreeding season biology. Furthermore, the limiting factors and regulatory mechanisms that determine abundance remain poorly understood for most bird species. Pete Marra, Director of the Smithsonian Migratory Bird Center, uses long-term research on redstarts in Jamaica to show how conditions on wintering grounds, such as climate and habitat, affect both arrival time and body condition of individual birds on breeding areas, and how these parameters are likely to have important consequences for breeding events and annual survival. Understanding how global change will influence migratory organisms requires the study of biological phenomena in the context of the entire annual cycle.
