Migration of Birds
Nature Bulletin No. 146 March 13, 1948
Forest Preserve District of Cook County
William N, Erickson, President
Roberts Mann, Supt. of Conservation
MIGRATION OF BIRDS
High in the sky, wild geese are honking as they return to their nesting
ground in the far north. Presently, our summer songbirds will appear
and the ponds and marshes be repopulated by ducks and shore birds.
Some birds, like the juncos and tree sparrows, resident here all winter,
will leave for Canada or our northern states, in May, great flocks of
warblers will arrive, tarry briefly, and pass on, not to be seen again until
they migrate southward in autumn.
The spectacular annual journeys of many kinds of birds, and their
homing "instincts", have been a source of wonder since ancient times.
In recent years, large-scale marking with small aluminum identification
bands upon their legs, has yielded much information about birds their
migration routes, speed of travel, summer and winter homes, length of
life and life histories.
Many of our summer residents, including the robing and wrens, spend
the winter in southern states. Others travel to Central and South
America. The bob-o-link winters in Argentina. Some warblers nest in
northern Canada or Alaska and winter in Brazil, traveling 5,000 miles
to do so. Our tiny ruby-throated hummingbirds fly across the Gulf of
Mexico to Central America. The golden plover, in fall migration flies
non-stop nearly 2500 miles across the ocean from Nova Scotia to South
America. But the champion long distance flyer is the Arctic tern, which
travels from Labrador where it nests, across the Atlantic Ocean to
Europe and then down to the Antarctic, at the southern tip of South
America. Each year it makes a round-trip of 22,000 miles.
The shortening of the daylight hours, cooler weather, and the decrease
in their food supply, probably have much to do with the fall migration
of many birds. in spring, some scientists believe, the increasing hours of
more intense sunlight stimulate a gland which causes the bird to become
restless and start northward. But why it winters in one particular place
and summers in another, year after year, and how it finds its way
between them, traveling usually at night, is still a mystery.
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Update: June 2012