Abstract
Twice each year, the sky is filled with birds seeking new grounds for feeding and nesting. Amazingly, they don't even need a flight plan to know precisely when to leave or how to get there. Who hasn't thrilled to the sight of V-formations of migrating geese as they wing their way north to their nesting grounds, or heard them squawking overhead in autumn as they head back south to spend the winter in milder climates? This amazing, predictable movement occurs twice each year, involving millions of birds worldwide, traveling hundreds and even thousands of miles. Truly, "migration is the most spectacular of bird movements."