Bird migration is the regular seasonal journey undertaken by many species of birds. Bird movements include those made in response to changes in food availability, habitat, or weather. Sometimes, journeys are not termed "true migration" because they are irregular (nomadism, invasions, irruptions) or in only one direction (dispersal, movement of young away from natal area). Migration is marked by its annual seasonality.
In contrast, birds that are non-migratory are said to be resident or sedentary. Approximately 1800 of the world's 10,000 bird species are long-distance migrants.
Read more about Bird Migration: General Patterns, Historical Views, Long-distance Migration, Short-distance and Altitudinal Migration, Irruptions and Dispersal, Physiology and Control, Adaptations, Evolutionary and Ecological Factors, Ecological Effects, Study Techniques, Threats and Conservation
Famous quotes containing the word bird:
“Alas for the cripple Practice when it seeks to come up with the bird Theory, which flies before it. Try your design on the best school. The scholars are of all ages and temperaments and capacities. It is difficult to class them, some are too young, some are slow, some perverse. Each requires so much consideration, that the morning hope of the teacher, of a day of love and progress, is often closed at evening by despair.”
—Ralph Waldo Emerson (1803–1882)