Migration

Perhaps the most remarkable aspect of migration is the navigational skills employed by the animals. Birds such as the albatross (Diomedea sp.) and lesser golden plover (Pluvialis dominica) travel hundreds of miles over the featureless open ocean, yet unerringly home in on the same breeding grounds year after year. Salmon (Oncorynchus sp.) migrate upstream from the sea to the very same freshwater shallows in which they were hatched. Monarch butterflies (Danas plexippus), which began life in the United States or Canada, travel to the same wintering grounds in southern California or Mexico that had been used by ancestors many generations removed.

How are these incredible feats of navigation accomplished? Different animals have been shown to use a diverse range of navigational aids, involving senses often much more acute than our own. Sight, for example, may be important for some animals' navigational skills, although it may often be secondary to other senses. Salmon can smell the water of their home rivers, and follow this scent all the way from the sea. Pigeons also sense wind-borne odors and may be able to organize the memories of the sources of these smells in a kind of internal map. It has been shown that many animals have the ability to sense the magnetic forces associated with the north and south poles, and thus have their own builtin compass. This magnetic sense, along with the sense of smell, are believed to be the most important factors involved in animal migration, but researchers are continually discovering new and unusual navigational systems throughout the animal kingdom.