Magnetoreception, flexible use of cues and low-information navigation in animals.

Magnetoreception - the ability to detect Earth's magnetic field - is widespread among animals. Despite recent progress, fundamental gaps in our knowledge remain. The two main goals of modern magnetoreception research are to: (1) understand how magnetic information is used by animals in navigation; and (2) uncover the biophysical mechanisms that underlie magnetic field detection. The discovery that animals use magnetic information not only as a directional (compass) cue, but also as a kind of 'map', has revolutionized research in animal navigation. Recent findings suggest that animals use magnetic cues flexibly and idiosyncratically to help guide spatial movements. We propose that a valuable but seldom used approach to studying animal movements is to consider ways in which seemingly complex navigational feats can be accomplished with minimal information, often without the need for classical map-and-compass navigation, a cognitive representation of the environment, or prior knowledge of the terrain. We also used a recently developed model to demonstrate that natural selection can potentially 'tune' magnetic navigation systems to optimize navigation in different parts of the world, and we illustrate the possibility with examples of long-distance migrations by sea turtles, fishes and birds. Emerging evidence further implies that there are multiple magnetoreceptive mechanisms rather than a single, universal way of sensing magnetic fields. We argue that the path forward, for both unraveling animal navigation and elucidating mechanisms of magnetoreception, requires a thoughtful balance between a search for unifying principles and an expectation of major differences among species and populations.