Migratory birds are well known to navigate over long distances between feeding grounds and breeding sites, often over thousands of miles. Ornithologist G. V. T. Matthews demonstrated this in early studies of the Manx shearwater seabird. From a colony of shearwaters nesting on the island of Skokholm off the southwest coast of Wales. individual birds were transported away in various compass directions, including westward across the Atlantic Ocean and released. The birds were observed as they were released and many quickly showed significant orientation toward home, apparently based on the environmental features around them, even in an unfamiliar location. Most reached their nest sites on Skokholm far more rapidly than they could have done by random searching. Recently, highly sophisticated experiments have been undertaken using satellite tracking to monitor the activity of returning home, or homing behavior, of oceanic birds to which miniature radio transponders have been attached.

These forms of homing behavior are natural phenomena that resemble human navigation on land, by sea, or in the air, but without the use of human gadgetry. Shearwaters, and homing pigeons too, when taken to a locality with which they are unfamiliar seem able to determine their correct homing direction quite quickly, with reference only to cues available to them in the novel locality. One possible explanation for this is that they are able to make a comparison between astronomical information, such as the position of the sun, moon. or stars at the new locality compared with home at a particular time of day. To make such a comparison they would require a biological clock that signaled to them where, say, the sun should be at a particular time of day at home, compared with its observed position and apparent orbit in the new locality. Then, having established their position in relation to home they would also require some form of compass mechanism to permit them to establish the correct bearing (direction) to return.

An alternative hypothesis is that birds carry with them and are able to read some form of map. In that event they would still require a compass to navigate home, but they might not need a clock. One line of research along these lines postulates that oceanic birds have an awareness of the pattern of the Earth's magnetic field, a map that they carry and use to determine their homing directions. To test the hypothesis, experiments have been carried out on a number of oceanic bird species by attaching magnets to their bodies on the assumption that the birds would then be confused if they normally navigate in response to the Earth's geomagnetic field. Albatrosses, shearwaters. and petrels have all been tested in this way and all navigated over very long distances to their nesting sites as normal as if their navigation system was unaffected by the presence of an artificial magnetic field around them. However, notwithstanding the consistency of evidence so far against the hypothesis, it remains unresolved whether or not magnetic cues are involved in global navigation by oceanic birds

A search is also under way to determine whether some birds might also navigate by a form of olfactory map-a mental map of odors. Particular success in this approach has been achieved in studies of Leach's petrel which for some years has been known to navigate locally back to its nesting burrow using its sense of smell. More recently, too, the same species of bird has been shown to be able to detect the smell of the volatile compound dimethyl sulfide, which is produced by many phytoplankton species that form the basis of marine plankton food chains. Productive areas of the ocean surface that are rich in phytoplankton and the planktonic animals that feed on it are favorite feeding grounds for Leach's petrels, attracted by the smell of dimethyl sulfide emitted copiously there. Evidence that this form of navigation by the petrels has been perfected during evolution comes from experiments in which the sense of smell of a few birds was artificially and temporarily impaired and the affected birds were unable to show homing behavior when released over a feeding area. So, the apparently featureless surface of the ocean may present a varied olfactory landscape to marine birds with a keen sense of smell.