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Natal homing, or natal philopatry, is the homing process by which some adult animals that have migrated away from their juvenile habitats return to their birthplace to reproduce. This process is primarily used by aquatic animals such as sea turtles and salmon, although some migratory birds and mammals also practice similar reproductive behaviors. Scientists believe that the main cues used by the animals are geomagnetic imprinting and olfactory cues. The benefits of returning to the precise location of an animal's birth may be largely associated with its safety and suitability as a breeding ground. When seabirds like the Atlantic puffin return to their natal breeding colony, which are mostly on islands, they are assured of a suitable climate and a sufficient lack of land-based predators.
Sea turtles born in any one area differ genetically from turtles born in other areas. The newly hatched young head out to sea and soon find suitable feeding grounds, and it has been shown that it is to these feeding areas that they return rather than to the actual beach on which they started life. Salmon start their lives in freshwater streams and eventually travel down-river and are washed out to sea. Their ability to travel back, several years later, to the river system in which they were spawned is thought to be linked to olfactory cues, the "taste" of the water. Atlantic bluefin tuna spawn on both the east and west shores of the Atlantic Ocean but intermingle as they feed in mid-ocean. Juvenile tuna that have been tagged have clearly shown that they almost invariably return to the side of the Atlantic on which they were spawned.
Various theories have been put forward as to how the animals find their way home. The geomagnetic imprinting hypothesis holds that they are imprinted with the unique magnetic field that exists in their natal area. This is a plausible theory but has not been proven to occur. Pacific salmon are known to be imprinted on the water chemistry of their home river, a fact that has been confirmed experimentally. They may use geomagnetic information to get close to the coast and then pick up the olfactory cues. Some animals may make navigational errors and end up in the wrong location. If they successfully breed in these new sites, the animal will have widened its breeding base which may ultimately increase the species' chances of survival. Other, unknown means of navigation may be involved, and further research is needed.