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
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