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.
Let's start by looking at the general features of a weather map.
How to Read a Weather Map
by looking at the general features of a weather map. 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.
The air around a low pressure system moves counter-clockwise. The colored
lines represent fronts: dividing lines between cold and
warm air. Blue lines represent
with warm air in front (to the right of) the line and cold air behind
(to the left of) the line. The red line
is a warm front, with colder
air in front of it and warm air behind.
what does this all mean for birds? Watch the High Pressure
Birds want to fly with a tailwind to help them travel
farther. In the spring, this means winds moving south to north. Headwinds,
or winds 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. Since highs follow cold fronts, birds will
be forced 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 again.
birds can land in huge numbers (in the hundreds or even thousands) in
what is known as a fallout. Fallouts can be quite impressive
to see, and large fallouts are common along the Gulf Coast because birds
have been flying non-stop for 18 hours, and are already exhausted when
they arrive. Headwinds or rain make the situation even worse. Since highs
(H)follow cold fronts, birds
will be forced 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 again.
So why don't birds use low pressure systems (L)?
Low pressure systems often bring bad weather with them. Even though the
winds may be right, flying conditions are not good.
Your Skills With Today's Weather Map
While it is too early to see any major migratory flights, let's
practice reading the weather map and seeing how it might affect migration.
cold front that moved across the country and brought those big storms
would have force many migrants to land. There is now a low pressure area
over the eastern US, and high pressure over the Midwest. The low pressure
area doesn't have much rain with it, so that means migrants forced to
land by the storms would now be able to take off again because they would
have tail winds, but no rain. Migrants farther west, however, would still
be grounded until the high moves east, and bird watchers could expect
to see lots of birds. What's in store?
cold front is moving into the West Coast.
in the West will be forced to land because of the bad weather.
a couple of days, the front will be in the Midwest and western
Gulf area, and people there could expect to see a fallout.
the end of the week, it will be the eastern US that would see migrants
Starting to Arrive!
I have been getting reports of swallows and martins across
are some of the first migrants to arrive in the spring,
so it won't be long before migration really gets going.
Dust off your binoculars and start looking! Take care.
North Chickamauga Creek Conservancy