Birds and
the Built-in Barometer
Eagles
are very aware of their environments. Their activities are dictated by
the natural rhythms of light and dark, heat and cold, and wet or dry.
Their extremely sensitive bodies can even feel the smallest changes in
air pressure to help them cope with the weather and changing seasons.
Did you know:
- Migrating
birds are excellent weather forcasters. Because they are sensitive
to air pressure they time their migratory flights to favourable weather
conditions.
- Barometric
pressure is the pressure exerted by the atmosphere and measured using
a "barometer."
- Changes
in pressure are more important than exact readings - a downward trend
is a general predictor of stormy weather and an upward trend suggests
fair weather.
- The normal,
average sea-level pressure is about 29.92 inches, which means the barometer's
needle will rest near 30.
Scientists
also have known for a long time that migrating birds fly at different
altitudes than non-migrating birds, and maintain this altitude even on
moon-less nights when they can't see the ground at all. How do they maintain
a particular altitude? Many scientists suspect that this is also due
to their ability to "feel" air pressure.
Recognizing
air pressure is also handy because birds often migrate along frontal
systems, and changing air pressure is one of the first signs that a front
is coming. Just as low pressure indicates storms, high pressure systems
typically have clear skies. Thus, sensing if air pressure is rising or
falling would enable a bird to anticipate changes in weather.
How do birds
judge air pressure? Scientists don't know!! They do have a couple of
guesses. One is that birds may be able to detect it through their inner
ear. We detect large changes in air pressure in our own inner ear when
we make a fast change in altitude--that's when our ears "pop." Another
guess is that the birds detect air pressure somehow though the huge air
sacs that connect to their lungs and fill much of the space inside their
bodies.
Try
This!
Watching Barometric Pressure and the Weather and Birds
1) Watch how barometric pressure changes with the weather. Record the barometric
pressure over a period of at least 3-4 days. (Take a reading regularly, as often
as 3-4 times during the school day. Ideally students could also be assigned to
keep these records during off-school hours for these 3-4 days.) Tip: Keep your
eye on the weather map! Try to time this activity when a storm is approaching.
3) After observing
how pressure changes over time, study weather maps and track high & low
pressure systems, and their associated wind directions and fronts. Try
to do this for a week or two, to see the patterns.
2) Set up
an experiment to see if pressure changes affect bird behavior in your
favorite bird feeding location. Fill your bird feeders and count the
birds you see for a period of time each day. Record barometric pressure
each day. Analize your information and then answer this: Does your data
agree with many scientists - that birds more actively feed when pressure
falls? Why do you think they behave this way?
Reading Strategy
Spotlight: Paraphrase/Retell
Reading
and Writing Connections >>
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The discussion
of barometers and weather includes new words and concepts that are complicated
for many people. Paraphrasing helps readers check their own comprehension.
Paraphrasing is restating or explaining ideas in your own words while retaining
the meaning and ideas in the original selection. Here are questions that
will help readers paraphrase information:
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