Genetics, Not Weather, Informs Migration Behaviors in a Long-Distance Migrant Songbird

Migration is the riskiest portion of the annual breeding cycle, with long-distance migratory birds enduring long periods of varied landscapes, dangerous weather, and geographical barriers such as long stretches of open water. Therefore, birds utilize a combination of both innate (i.e., genetic) and environmental cues to maximize their chances of survival during migration. Studies have suggested that short-distance migrants are more likely to adjust migration timing to match non-endogenous cues like local weather conditions, while long-distance migrants rely heavily on genetically-ingrained behaviors to determine the start of spring migration. While many studies have examined the effects of environmental variables and genetics individually, few have examined the combined effects of these influences throughout the annual cycle of a migratory songbird species. We examined the correlation of both genetics and the environmental conditions experienced by a long-distance migrant, the Bobolink (Dolichonyx oryzivorus), with the timing and latitude of seven migratory events throughout their annual cycle. To our knowledge, this is the first study to document the possible effects of genetic relatedness throughout the annual cycle of a long-distance migratory songbird using neutral genetic markers. Genetic relatedness was highly correlated with the timing (4 of 7) rather than latitude (1 of 7) of migration events. Departure from pre-water crossing stages, arrival to wintering grounds and departure from South America were the only migration events in the annual cycle where neither the timing nor location of the event were correlated with genetic relatedness. While weather had significant effects at several points in the annual cycle, these trends were often correlated with differences in latitude or timing between males and females. This study provides direct support for the long-held theory that long-distance migrants largely rely on innate behavior instead of environmental conditions to inform migration decisions.