Cues, strategies, and outcomes: how migrating vertebrates track environmental change

Migratory vertebrates adjust their movements in response to environmental change. Throughout their migrations, they gather information, integrate environmental and internal state data, and make decisions about the timing and orientation of migratory movements. Understanding this class of animal decision-making has both basic and applied interest because migratory animals face unique challenges adjusting to anthropogenic environmental changes worldwide. Evolved changes in decision mechanisms necessarily lag behind environmental changes because their evolution is driven by the consequences of resulting actions, and this raises the possibility of major mismatches between behaviour and environmental circumstances when the latter change faster than the pace of natural selection. Yet, migration-decision systems have the capacity for considerable flexibility at the phenotypic level. Distinguishing the evolution of fixed genetic changes from changes that can occur in individual phenotypes requires a better understanding of the mechanisms underlying organismal response. We reflect on such issues, hoping to engender new thinking about the special difficulties that seasonally migrating animals face in times of rapid environmental change. We focus on three key aspects: (1) We distinguish between variations in migratory timing forced upon migrants by overwhelming environmental changes and those that arise from individual “strategic” variation in decision-making. (2) We examine how the availability and reliability of information about environmental quality determine optimal cue choice and cue-response. (3) We highlight how adjustments of individual migration strategies can be made by changes in the decision-making machinery during development, dramatically increasing the rate at which migratory strategies can adjust to environmental change.