Differential Migration

The timing of migration within a species can differ between birds of different age and sex groups; this phenomenon is referred to as differential migration. Typically during spring migration males depart tropical wintering areas and arrive at temperate breeding areas earlier than females. While species that deferentially migrate might experience reduced competition en route, current hypotheses for this behavior focus on reproductive success of individuals. These hypotheses include: males arriving first to claim the best territories, males arriving earlier to maximize mating opportunities, females arriving later to minimize time waiting for mates, and females being better able to assess male fitness by quality of territory. While differential migration seems to be advantageous, not all species are thought to exhibit it. 

In an effort to determine the prevalence of this behavior, we utilize a 20-year data set to examine passage date in several songbirds species during their spring migration along the Gulf of Mexico coast.