by Stephen James O'Meara
From whales to butterflies, animals around the globe are on the move. Who hasn't noticed geese flying south for winter, or the seasonal appearance of whales off our coasts? Who isn't aware of the almost clockwork-like appearance and disappearance of certain species of birds in the spring and fall?
While most of us anticipate the comings and goings of the animals that visit our neighborhoods, some scientists are gaining a more global perspective on the seasonal mass movements of animals, known as migrations. Millions of creatures undertake these extraordinary journeys of survival each year. Here are some of the most mysterious—and perhaps most unknown—amazing migrations.
Great White Sharks
Great White Sharks mysteriously appear each spring along the U.S. coast of the north Pacific, in an area called the “Red (Blood) Triangle.” No one knows where they come from. They arrive in early April, at the Farallon Islands, 48 kilometers west of San Francisco, where they feed on newborn seal pups. The sharks then swim south to the Channel Islands off the coast of Los Angeles, where they give birth. Come summer, the sharks circle northward to Ano Nuevo Island (just south of the Farallons) before they migrate to southern Alaska. What happens after that? No one knows.
Arctic Terns are the undisputed “migration marathon” champs. Each year, they fly from the Arctic to the Antarctic—a roundtrip of 32,000 to 40,000 km. They leave the Arctic in the fall, flying eastward across the Atlantic and then southward along the west coast of Europe and Africa, until they reach the Antarctic Ocean. In the spring, they return along the east coast of South and North America. Because the terns are in both the Arctic and Antarctic during the periods of the longest days, they see more daylight than any other living creature!
Desert Locusts hold the record for the longest insect movement. Migration in insects serves not only for escape from old habitats but also for reproduction and colonization in new ones. Each year, seasonal winds carry these breeding insects from the west coast of Africa, at Mauritania, to as far west as the West Indies—a distance of 4,500 km. Others have reached the east coast of South America. In fact, some probably traveled thousands of kilometers from their habitats in north Africa before they began their trip across the Atlantic.
Red Crabs of Christmas Island in the Indian Ocean make one of the most bizarre migrations known. At the beginning of the wet season (usually October through November), some 120 million of these land crabs scurry from the forest to the sea, where they breed and lay eggs. The crabs travel more than 90 meters in an hour to prevent dehydration in the hot sun. The three-week journey involves climbing down high cliff faces, marching through human settlements, and crossing streams and highways. If caught in unshaded heat, the crabs die; about one million are killed crossing streets. The migration is linked to the phases of the moon, so that eggs may be released into the sea precisely at the turn of the high tide during the last quarter moon.
Green Turtles leave their feeding grounds off the coast of Brazil to begin a remarkable 2,000-km roundtrip journey to tiny and remote Ascension Island in the south Atlantic. Adult turtles make this journey every three to four years. The turtles swim for six weeks through open ocean to nest, it appears, on the very beaches where they were born. After their young are born, the turtles return to the coast of Brazil. The method by which the turtles find Ascension Island is not fully understood, and is considered one of the most amazing navigational feats of all species in the animal kingdom.
Loggerhead Turtles migrate in enormous circles in both the Atlantic and Pacific oceans. The Pacific route takes them from Japan to Mexico and back again. That's a 30,000-km roundtrip, and one of the longest migrations recorded. (It is longer than the 20,000-km roundtrip of gray whales on their annual voyage between Mexico and the Arctic.) A third of Japan's loggerhead turtles nest on Yakushima Island. One of them, which had spent a year at the Okinawa Aquarium before being tagged and released in 1988, was recaptured six years later…in Mexico!
Zebras, Gazelles, and Wildebeests
Every year, around the end of the wet season in April, Africa's Serengeti Plain is the site of the greatest wildlife show on Earth, as some 200,000 Zebras, 500,000 Gazelles, and 1.5 million Wildebeests follow the rains and cross some of the continent's most spectacular landscapes. The main migration starts in Tanzania's Ngorongoro Conservation Area and the southern Serengeti, where the animals calve between January and mid-March. The migration then heads north into the Serengeti's western corridor, almost as far as Lake Victoria. When the grass supply has been exhausted, usually at the end of May, the herds move farther north to the Kenyan border before returning to their breeding grounds. by the time they arrive, the grounds are once again green and lush. In the end, the animals will have covered thousands of kilometers—that's if they successfully avoid the multitude of lions, leopards, cheetahs, crocodiles, wild dogs, and hyenas, who must see the great migration as a super-value meal!
- This article mentions several types of animals that migrate for various reasons. Why do animals migrate to breed? What might be some of the benefits in traveling, sometimes thousands of miles, to breed? Write a few sentences explaining what you think some of the benefits might be.
[anno: Answers will vary but could include opinions about a more abundant food supply and fewer natural predators in breeding grounds.]