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Re: Migration/ Weather question





Hi Shelley-
Fall and spring migration seem to differ in the relationship between fronts and
birds.
Birds generally like to migrate when the weather is clear, and there are no
strong head winds that would affect their ability to cover long distances on a
finite amount of energy (read fat reserve).  This is why migrants "fall out"
when their migration path collides with rain or an area of dense could.  Rainy
weather can actually produce the best numbers of migrants as they are forced
down wherever they happen to be.
Spring migrants like to see southerly winds where the prevailing breezes tend to
push them along in the direction they want to go.  In relation to a front,
southerly winds usually occur in the warm sector which precedes a cold front.
In other words the birds follow along behind the warm front.
Fall is rather different.  The birds want clear skies and northerly winds.
These conditions usually occur in our area after the passage of a cold front.
In our area north-westerly winds are considered the prime breezes to bring
migrants.  The reason for this probably relates to our geography.  As we are on
the east coast, and many of the migrating bird are flying from north or
northwest of here, northwest winds will tend to bring the most migrants.
However, the passage of a cold front does not always lead to the best migrant
birding.  The weather conditions may be so favorable that the birds do not stop
in our area at all.  They may fly along for another 200 miles and bring our
South Carolina friends some nice migrants.  In fact, during Sept in Raleigh, my
best migrant counts were immediately after the remains of a tropical system
moved through, the cold front last week was rather disappointing.  Nonetheless,
the day or two following passage of a strong cold front are often considered to
be prime migrant watching times.  Of course the drawback is that all of those
northerly winds are whipping the already yellowish leaves around and making it
hard to see all of those little 5 inch birds!!

Best,
Steve Shultz
Cary, NC





Psbmt@aol.com on 10/03/2000 11:06:49 AM





To:   carolinabirds@duke.edu
cc:
Subject:  Migration/ Weather question



This is probably pretty elementary to a lot of you, but I'm not sure how to
read cold fronts as far as the optimum time to look for migrants.  I'm
thinking about the next few days with the big weather changes here, and
wondering if most of the migrant birds pass through just ahead of the front
say on Thurs. while it's still warm, or on Fri. as the temp. drops somewhat
and the front is actually passing through, or on Sat. or later after the
temp. really plunges behind the front.  I guess the month and how close it's
getting to the end of migration could also be a factor...
Thanks,
Shelley Theye

Shelley Theye
North Chatham County, NC
Psbmt@aol.com

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