Introduction

Migration

Long-distance migration has evolved in many species and continues to remain a plastic trait as indicated by ever-changing migratory patterns.  In general, migration is seen as a strategy to cope with continual, and often rapid changes in the environment.  Factors that may drive species migration include: seasonality, temporal distribution of resources, habitats, and predation.  There exist many ways in which organisms may accurately navigate during long-distance migrations such as the use of patterns from the sun and the stars, and even orientation using the earth's magnetic field. [1] The latter system of navigation will be the focus of this website.

 

The Earth's Magnetic Field

The earth's magnetic field can be roughly equated to the field produced by a bar magnet, with the field lines coming from the north pole and going into the south pole.  This analogy is not completely correct because the earth's magnetic field is created not by the organized orientation of the electrons and nuclei of the iron atoms within the earth's core, but due mostly to electric currents in the earth's outer core.  Another oddity of the earth's magnetic field is that its poles drift independently over an average geographical area of 15km per year. The key features of the earth's magnetic field which can be used to determine global position are the angle
of intersection of  the magnetic field and     the surface of the earth,which range from 0° at the equator to 90° at the poles, and the intensity of the magnetic field, which is weakest at the equator and strongest at the poles. [3]                     


A Representation of the Earth's magnetic field [11]


Model Organisms

It has been suggested in recent studies that many vertebrates are sensitive to the earth's magnetic field, which thus provides a navigation system which can be used for migratory purposes.  It is believed that some species may use the earth's magnetic field as a sort of internal compass which allows them to orient themselves directionally, while other species may use the earth's magnetic field to create an internal map which allows them to orient themselves positionally relative to a destination.  Such systems have been shown to exist in organisms ranging from mollusks and lobsters, all the way to birds and sea turtles.