Migration is the process during which animals move from one habitat to another, then return to their original home. All sorts of animals migrate, including species of fish, amphibians, reptiles, insects, mammals, and birds. Species may migrate due to the changing seasons, to find food, or for reproductive reasons. True migration patterns involve either a seasonal pattern or a major habitat change—conditions that some traditional human migration also fits. Animals use environmental cues such as the magnetic pull of the earth and the position of the sun to know when they should leave and which direction they should go.
Species from all classes of animal migrate, and often, the most memorable examples are types of birds. Many species of bird migrate, normally between the northernmost and southernmost extent of their ranges, and the distance they travel varies greatly between species—the Arctic tern (Sterna paradisaea), which boasts the longest migration, spends the northern hemisphere’s summer in the Arctic and the southern hemisphere’s summer in the Antarctic. Avian migration is triggered mainly by changes in day length, and birds use celestial cues from the sun, moon, and stars, Earth’s magnetic field, and their own mental maps to navigate.
This map layer shows the migration pattern of a bird species called the sandhill crane (Antigone canadensis), which travels from the southern United States to the Arctic each spring to breed. Every year, hundreds of thousands of the birds (80 percent of sandhill cranes in North America) pass through the central United States, making their way out of the state of Texas through the states of Oklahoma, Kansas, Nebraska, and North and South Dakota. You can see these patterns on the map layer: the cranes’ normal distribution is in red, and the areas where they breed are purple. The orange streak through the middle of the United States and Canada shows the path they take between these two locations every spring.
In addition to migration for reproductive reasons, many species living in regions with seasonal temperature change migrate to warmer areas when the temperatures drop. Monarch butterflies (Danaus plexippus) relocate each winter, the only species of butterfly known to make a two-way migration like birds do, some flying as far as 4,828 kilometers (about 3,000 miles)! Another reason for animal migration is to find food, and by far the largest example of this is the great Serengeti wildebeest (Connochaetes) migration. Every year, over a million wildebeest and 300,000 zebras (subgenus Hippotigris) move through the area in search of grass to eat, guided by rain and growth of new vegetation. They begin the large, circular motion in the spring and move clockwise through the region, arriving back to their original habitats near the end of the year.
During their journey through North America, sandhill cranes interact with a variety of threatened species and ecosystems. In order to protect these vulnerable parts of nature and raise awareness of the hazards they face, National Geographic Explorer and world-renowned Photographer Stephen Wilkes has partnered with Canadian Geographic and Parks Canada in a new initiative to reconnect people with nature, highlight an increasing number of threatened Canadian species and spaces, think in a global sense when it comes to responsible habitat conservation, and encourage people to action. In 2017, Wilkes experienced the sandhill crane migration himself, capturing the photo The Epic Journeys of Migratory Birds.
