Birds, butterflies, fishes, and sea turtles are among the many animals that travel long distances and then return home to reproduce. Recent DNA tests confirm that loggerhead sea turtle hatch on Florida beaches along the Atlantic, then swim hundreds of miles across the ocean to the Mediterranean Sea. Several years later, those that survive to become adults navigate back, often to the same beach, to lay their eggs.
Green turtles (Chelonia mydas) migrate more than 2000 kilometers (1200 miles) across open ocean between their feeding area off the coast of Brazil and their nesting place on Ascension Island, a tiny island less than 10 kilometers (6 miles) wide. There, each turtle will make three to seven trips, about 12 days apart, from the water to an isolated beach, laying about 100 eggs in the sand each time.
Why do animals migrate? Migration is a very precise evolutionary adaptation to seasonal changes in climate, availability of food resources, and safe nesting sites. The dramatic annual migration of millions of monarch butterflies from Eastern Canada and the United States to Mexico – a 2500-kilometer journey (about 1500 miles) for some – appears to be related to the availability of milkweed plants on which females lay their eggs. In cold regions these plants die in late autumn and grow again with the warmer weather of spring. The wintering destinations of monarchs also seem to be determined by temperature and humidity.
The benefits of migration are not without cost. Many weeks may be spent each year on energy-demanding journeys. Some animals may become lost or die along the way. And migrating individuals are often at greater risk from predators in unfamiliar areas. In recent years, human activities have interfered with migrations of many kinds of animals. For example, after millions of years of biological success, survival of the sea turtles is threatened by the fishing and shrimping industries. As they migrate, thousands of turtles drown each year in the nets of shrimpers and fishermen.
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"Why do animals migrate?" was posted on Wednesday, October 17th, 2007 at 11:44 am.
What kinds of animals migrate?
Why do turtles migrate?