Different kinds of animals migrate in different ways.
In birds Approximately 1,800 of the world's 10,000
bird species migrate long distances each year in response to the seasons. Many of these migrations are north-south, with species feeding and breeding in high northern latitudes in the summer and moving some hundreds of kilometres south for the winter. Some species extend this strategy to migrate annually between the Northern and Southern Hemispheres. The
Arctic tern has the longest migration journey of any bird: it flies from its
Arctic breeding grounds to the
Antarctic and back again each year, a distance of at least , giving it two summers every year. Bird migration is controlled primarily by day length, signalled by hormonal changes in the bird's body. On migration, birds
navigate using multiple senses. Many birds use a sun compass, requiring them to compensate for the sun's changing position with time of day. Navigation involves the ability to
detect magnetic fields.
In fish migrate up rivers to
spawn Most fish species are relatively limited in their movements, remaining in a single geographical area and making short migrations to overwinter, to
spawn, or to feed. A few hundred species migrate long distances, in some cases of thousands of kilometres. About 120 species of fish, including several species of
salmon, migrate between saltwater and freshwater (they are 'diadromous').
Forage fish such as
herring and
capelin migrate around substantial parts of the North
Atlantic ocean. The capelin, for example, spawn around the southern and western coasts of Iceland; their larvae drift clockwise around Iceland, while the fish swim northwards towards
Jan Mayen island to feed and return to Iceland parallel with Greenland's east coast. In the '
sardine run', billions of Southern African
pilchard Sardinops sagax spawn in the cold waters of the
Agulhas Bank and move northward along the east coast of
South Africa between May and July.
In insects '' dragonflies, known as globe skimmers, in
Coorg, India Some winged
insects such as
locusts and certain
butterflies and
dragonflies with strong flight migrate long distances. Among the dragonflies, species of
Libellula and
Sympetrum are known for mass migration, while
Pantala flavescens, known as the globe skimmer or wandering glider dragonfly, makes the longest ocean crossing of any insect: between India and Africa. Exceptionally, swarms of the desert locust,
Schistocerca gregaria, flew westwards across the Atlantic Ocean for during October 1988, using air currents in the
Inter-Tropical Convergence Zone. In some
migratory butterflies, such as the
monarch butterfly and the
painted lady, no individual completes the whole migration. Instead, the butterflies mate and reproduce on the journey, and successive generations continue the migration.
In mammals Some mammals undertake exceptional migrations;
reindeer have one of the longest terrestrial migrations on the planet, reaching as much as per year in North America. However, over the course of a year,
grey wolves move the most. One grey wolf covered a total cumulative annual distance of . s in
Lesotho practice
transhumance with their flocks. Mass migration occurs in mammals such as the
Serengeti 'great migration', an annual circular pattern of movement with some 1.7 million
wildebeest and hundreds of thousands of other large game animals, including
gazelles and
zebra. More than 20 such species engage, or used to engage, in mass migrations. Of these migrations, those of the
springbok,
black wildebeest,
blesbok,
scimitar-horned oryx, and
kulan have ceased. Long-distance migrations occur in some batsnotably the mass migration of the
Mexican free-tailed bat between Oregon and southern Mexico. Migration is important in
cetaceans, including whales, dolphins and porpoises; some species travel long distances between their feeding and their breeding areas. Humans are mammals, but
human migration, as commonly defined, is when individuals often permanently change where they live, which does not fit the patterns described here. An exception is some traditional migratory patterns such as
transhumance, in which herders and their animals move seasonally between mountains and valleys, and the seasonal movements of
nomads.
In other animals Among the reptiles, adult
sea turtles migrate long distances to breed, as do some amphibians. Hatchling sea turtles, too, emerge from underground nests, crawl down to the water, and swim offshore to reach the open sea. Juvenile
green sea turtles make use of
Earth's magnetic field to navigate. s on annual migration Some crustaceans migrate, such as the largely-terrestrial
Christmas Island red crab, which moves en masse each year by the millions. Like other crabs, they breathe using gills, which must remain wet, so they avoid direct sunlight, digging burrows to shelter from the sun. They mate on land near their burrows. The females incubate their eggs in their abdominal brood pouches for two weeks. Then they return to the sea to release their eggs at high tide in the moon's last quarter. The larvae spend a few weeks at sea and then return to land. ==Tracking migration==