Birdwatchers flock to our coastal shores and wetlands in autumn to
observe the flocks of migrating birds.
Coos County birders watch as fall and winter bring an increase in many
kinds of ducks, gulls, and shorebirds, as well as a decrease in various
kinds of small birds, such as warblers, hummingbirds, and swallows.
These patterns may vary greatly even among related species: winter
wrens are year-round residents here, while house wrens breed in our region
but spend winters in the south; Anna's hummingbirds reside in Coos County
year-round, but Rufous and Allen's hummingbirds fly south for the winter.
While many animals regularly move from place to place—including certain
butterflies, bats, sea turtles, fish, and, whales—birds seem to catch most
of our interest. The seasonal migration most familiar to us is
wintering in warm tropical or neotropical environments, then moving north to
higher latitudes in the summer to breed. That migration is so familiar
we use it in every-day speech when we call humans who escape cold northern
winters "snow birds."
How do migrating birds find their way?
The sun's location in the sky is one bird navigation tool. However,
where you're headed can't be determined simply by knowing the location of
the sun: you also need a clock. (If you couldn't tell the
difference between 9am and 4pm, you'd end up traveling in great arcs.)
Necessarily, sun-navigating birds also have internal clocks.
In fact, the sun also spurs migrants' physical preparation: birds
begin to add fat and become more restless as the day length changes.
Sunlight is polarized by the atmosphere, creating designs visible to at
least some birds and used as a navigation tool.
Many species of birds migrate only at night, guided by the stars.
Turns out that it's the relative arrangement of stars that birds use to
navigate, not individual points. And, it appears that star-navigating
birds must learn the arrangement.
Like Scouts using a compass, many birds use the earth's magnetic fields
to get a fix on direction. Such birds may have physical compasses (perhaps
due to iron-rich crystals found associated with their nervous systems) or a
special visual ability to "see" the field.
In mapping migration routes of some birds, it's clear that geographic
features are also sometimes used to navigate, since some species follow
shorelines or trace major rivers during their migration.
Different species of birds use different techniques, and some are better
at those techniques than others.
And, each technique has drawbacks—for example, clouds can obscure the
stars above or landforms below. Navigation is most reliable for birds
using a combination of several methods.
Navigating during migration appears to be instinct reinforced by
experience. The instinct is clear for species in which first year and
experienced birds depart at different times. (In some species, too,
males and females travel separately.) The value of experience shows up
in cases where practiced migrants adjust to being moved far off course,
whether forced off-course by storms or by researchers.
Migration and migration routes apparently evolved over many generations,
spanning major climatic and geologic change. It seems those changes
are the reason certain species may take different routes on the northern and
southern journeys, and routes may or may not be direct.
More than simply "flying south for the winter," seasonal bird
migration we anticipate is not as straight-forward as it may appear.
Visit our pages on related topics:
gray whale migration
watching gray whales
Christmas Bird Count
A great deal of information on bird migration is available
at the Northern Prairie Wildlife Research Center website.
Wavecrest Discoveries can craft your personal discovery of this
delightful part of our world by customizing one of our distinctive guided
excursions. Our walks, tours,
and special activities are wonderful ways to
explore this fascinating region—and are the
perfect entertainment for guests.
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