Study of Bird Migration

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Study of Bird Migration

By | December 2012
Page 1 of 26
A flock of Barnacle Geese during
autumn migration
Example of long distance bird
migration routes.
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. [1]
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. [ citation needed]
General patterns
Flocks of birds assembling before
migration southwards (probably
Sturnus vulgaris)
Migrating waders in Roebuck Bay,
Western Australia
Many bird populations migrate long
distances along a flyway . The most
common pattern involves flying north in
the spring to breed in the temperate or
Arctic summer and returning in the
autumn to wintering grounds in warmer
regions to the south. Of course, in the
Southern Hemisphere the directions are
reversed, but there is less land area in
the far South to support long-distance
migration.
The primary motivation for migration
appears to be food; for example, some
hummingbirds choose not to migrate if
fed through the winter. Also, the longer
days of the northern summer provide
extended time for breeding birds to feed
their young. This helps diurnal birds to
produce larger clutches than related
non-migratory species that remain in
the tropics. As the days shorten in
autumn, the birds return to warmer
regions where the available food supply
varies little with the season.
These advantages offset the high stress,
physical exertion costs, and other risks
of the migration such as predation.
Predation can be heightened during
migration: the Eleonora's Falcon , which
breeds on...
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