For over a century, people have been banding birds (or ringing them as it is called in Europe) to determine their longevity, breeding and wintering areas, and routes of migration. Report Recovery of a Bird with a Metal Leg Band 1-800-327-BAND Or Submit Electronically.
From Wikipedia: Migration is the regular seasonal movement, often north and south along a flyway, between breeding and wintering grounds. Many species of bird migrate. Migration carries high costs in predation and mortality, including from hunting by humans, and is driven primarily by availability of food. It occurs mainly in the northern hemisphere, where birds are funnelled on to specific routes by natural barriers such as the Mediterranean Sea or the Caribbean Sea.
Historically, migration has been recorded as much as 3,000 years ago by Ancient Greek authors including Homer and Aristotle, and in the Book of Job, for species such as storks, turtle doves, and swallows. More recently, Johannes Leche began recording dates of arrivals of spring migrants in Finland in 1749, and scientific studies have used techniques including bird ringing and satellite tracking. Threats to migratory birds have grown with habitat destruction especially of stopover and wintering sites, as well as structures such as power lines and wind farms.
The Arctic tern holds the long-distance migration record for birds, travelling between Arctic breeding grounds and the Antarctic each year. Some species of tubenoses (Procellariiformes) such as albatrosses circle the earth, flying over the southern oceans, while others such as Manx shearwaters migrate 14,000 km (8,700 mi) between their northern breeding grounds and the southern ocean. Shorter migrations are common, including altitudinal migrations on mountains such as the Andes and Himalayas.
The timing of migration seems to be controlled primarily by changes in day length. Migrating birds navigate using landmarks, celestial cues from the sun and stars, the earth’s magnetic field, and perhaps mental maps. Some apparently use their sense of smell and there is some indication that infrasound may play a role in navigation.
Bird Migration and Navigation
Bird Migration Facts
Hawk Migration Association
Migratory Bird Day
Migration of Birds
Migratory Birds Program- The Nature Conservancy
Migration Watch (GB)
Mystery of Migration
Nine Awesome Facts About Bird Migration
Partners in Flight
Radar Ornithology Lab- Clemson University
Seeking Rest During Migration is Tiring
Smithsonian Migratory Bird Center
Spring and Fall Migration Timetables
The Epic Journeys of Migratory Birds
USFWS Division of Migratory Bird Management