Mechanisms of animal global navigation: Comparative perspectives and enduring challenges

Animals navigate over a range of distances, but it has been the global navigation of species migrating among spatially restricted, seasonal homes separated by thousands of kilometers that continues to defy a thorough mechanistic explanation. We survey the navigational behavior of migratory salmon, whales, sea turtles, and birds, as well as dispersing monarch butterflies, to promote the idea that an explicitly comparative approach to global navigation can provide insight into the evolution and properties of navigational mechanisms. The navigational abilities of migrant birds and sea turtles are used to illustrate the concepts of true navigation and vector navigation, leading us to consider the selective forces that might shape the evolution of navigational mechanisms. We propose that different navigational mechanisms, with different scales of accuracy, are likely employed during the course of migration. Furthermore, superficially similar global migratory behavior in different taxonomic groups is likely characterized by different sensory, representational and neural mechanisms reflective of group-specific adaptation to the physical properties of a migratory environment.