An additional trigger for birds to migrate is the need to breed to repopulatetheir species. Often, they return in the spring to procreatein the exact nesting spot they vacated in the fall. Birds certainly do qualify as creatures of habit!

The streamlinedbirds go to great lengths to make their migratory trips, sometimes flying as far as to other continents, or from the lowlandsto the highlands, or from the interior of a country to the seashore. The Arctic ternholds the long-distance medal for travel, as he travels from Antarctica to Massachusetts, logging up to 22,000 miles in stretches of up to 1,000 miles per week. Unfortunately, he does not rack upfrequent flyer miles! Most land-lubbersmake puddle-jumper like flights, with the exception of the American Golden Plover, who undertakes a non-stop, direct flight over the open expanse of ocean, from Nova Scotiato South America, without making one stop!

For some reason, most migratory birds schedule their annual departure and return dates close to, or on the same day, as in the previous year. Their timing, however, is not exact, as is the case with the legendary swallows of Capistrano, California. Reportedly, their annual migration begins like clockworkon October 23, and ends with their return on March 19. The legendary swallows sometimes do disappoint and vary their migratory schedule, much to the chagrin of the California Division of Tourism!

No scientific certainty exists as to how migratory birds establish their flight plans or patterns. They are not blessed with the bat's radar system, so fly-by-night birds have no physical landmarks to guide them, and those who make overseas flights have no landmarks to go by, even during the daylight hours. The most prevalent, plausible theory is that migratory birds sense the magnetic fieldsthat surround the earth, and guide their flights by these lines, which stretch from North to South. How else would young birds, who have logged no flight miles, successfully complete their migrations, especially in light of the fact that their mothers leave them in the dust, and begin their migrations first? Whatever the reason, neither snow nor rain nor heat nor gloom of night stays these birds from the swift completion of their annual migrations!

note: