Vulnerability and extinction risk of migratory species from different regions and ecosystems worldwi

Forty million miles of major roads crisscross the Earth's continents -- enough to circle the planet 1,600 times. For humans, these thoroughfares are a boon, enabling them to move with ease from place to place. But for migrating animals who are also hemmed in by dams, rivers, shipping lanes, urban development and agriculture, they create another barrier. As human development and activities continue to expand, scientists have grown increasingly concerned about such migrators, especially those tha