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Weather: A Bird's Eye View
by Dr. David Aborn
As I am sure you are aware, weather plays a very important role in bird
migration. This spring, I will teach you how to read a weather map to try to
predict areas of the country that might see large numbers of migrants landing.
Looking at a Weather Map
Let's start by looking at the general features of a weather map. The main
items you will want to look at are the blue and red lines, and the H's and
- The colored lines represent fronts, dividing lines between cold and warm air.
Blue lines represent cold fronts, with warm air in front (to the right of) the line and cold air behind (to the left) it.
The red line is a warm front, with colder air in front of it and warm air behind.
- The H's and L's represent high and low pressure centers, areas of swirling air. The air around a high pressure center circulates clockwise, whereas the air moves counter-clockwise around a low pressure system.
So what does all this mean for birds?
Watch the High Pressure Systems
Birds want to fly with a tailwind to help them travel farther. In the spring, this means winds moving south to north. Headwinds, wind moving north to south (in spring), make it too difficult for birds to fly, so they are forced to land. Bad weather, such as heavy rain, also forces birds to land.
- On the right side of a high pressure system, the winds are coming from the north, so migrants land.
- On the left side of a high pressure system, the winds are from the south, so birds take off to continue migration.
Since highs follow cold fronts, birds will be force to land immediately following the passage of a cold front.
After the high has moved east, usually a day or two later, the birds have tailwinds and take off.
Why Don't Birds use Low Pressure Systems?
The reason is that low pressure systems often bring
bad weather with them, so even though the winds may be right, flying conditions are not good.