~wildlife education~
Photo credit: istock.com/emilio100
Birds migrate to avoid the stresses associated with cold weather, and because of the greater availability of food and longer days in which to gather food for nestlings in warmer climes.
How birds fly these long distances is miraculous. For example, the Arctic tern will fly distances of up to 20,000km, and the Alaska-nesting Pacific golden-plovers embark on non-stop flights of over 8,000km. Birds prepare for their long trek by accumulating fat to provide fuel for the lengthy flight; they can lose a quarter to one-half of their body weight during overwater migration.
Most long-distance migrants, especially smaller birds, fly at night. They may travel continuously or land daily around sunrise to rest and forage. When traveling over water or unsuitable habitats, birds that normally stop each day may fly without a break for longer periods. Blackpoll Warblers migrate overland in spring, but autumn migrants travel non-stop over open ocean from south-eastern Canada and the north-eastern United States to their wintering grounds in South America. Migrants that move only relatively short distances usually travel during the day, generally spending only a few hours of the morning in migration. Aerial foragers, such as swallows and swifts, do not stop but simply feed in flight as they migrate.
Preparing to migrate, hummingbirds eat lots of nectar and insects and respond to hormonal changes triggered by changing daylight. Many ruby-throats fly non-stop across the Gulf of Mexico at least once a year.
How do the birds find their way to warmer climates? The process of migration has baffled humans for centuries, but many theories have been developed. Is it the sun, stars or the moon that helps to guide them, or landmarks or the earth’s magnetic field?
There are numerous bird migratory routes; some of them are simple and easily traced, while others are extremely complicated. Differences in distance traveled, in time of starting, in speed of flight, in geographical position, in the latitude of the breeding and wintering grounds, etc., all contribute to great diversity. No two species follow precisely the same path from beginning to end.
The four major North American flyways are the Atlantic, the Mississippi, the Central and the Pacific Flyways.
The continued loss and degradation of stopover habitat is a major threat to migratory birds; as forests are cleared and fragmented, birds have fewer places to rest on their arduous journey.
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