Date of this Version
Convection Effects on Nocturnally-migrating Birds 1-11
Seasonal bird migration occurs on large spatial scales and is influenced by many factors including weather conditions. Weather can include thunderstorms, which may force migrants to land or cause them to reroute a migration path. In this study, a sample of isolated thunderstorms was analyzed from the domains of three weather radars in the central United States to test hypotheses regarding the influence of thunderstorms on the distribution of migrants. Migrating bird density was often reduced in the wake of storms, and this wake reduction was typically more pronounced for larger, more intense and faster- moving storms, particularly in eastern Nebraska. Wind conditions more strongly influence the distribution and density of migrating birds in fall than in spring, providing evidence that migrating birds respond to environmental sig- nals more readily in the fall. This finding supports the concept that birds are more strongly obligated to cover distance in the spring and arrive in their breeding range on time. Wind conditions at the surface were generally more important to migrant density and distribution than wind conditions closer to flight level.