The complex process that enables animals to travel along a particular course in order to reach a specific destination. Navigation is an important aspect of behaviour in many animals, particularly those, such as birds, fish, and some insects, that undergo migrations. Landmarks, such as coastlines and mountain ranges, are important reference points for navigation but many animals can navigate successfully without the aid of these, by using the sun, stars, magnetic fields, odours, and polarized light. For example, birds use the sun and stars as landmarks and are sensitive to the earth’s magnetic fields, as are many other animals; for example, turtles return decades later to the beach where they hatched by sensing the intensity and inclination of the magnetic field (see magnetoreceptor), while salmon can identify the unique odour of their home river. It is thought that homing pigeons might use very low-frequency sound (infrasound) to build up a topographic map of the area surrounding their loft, as well as a magnetic sense, to guide their flight back home.