Date: Mon, 03 Apr 2000 22:03:27 -0400
Most birders are mindful of the weather in
relation to their field observation. Some are
attuned to the passing of cold and warm fronts
and the presence/absence of migrants every
spring and fall. But understanding the
correlation with specific bird movements
could benefit perhaps from a deeper look at the
type of systems that affect our weather.
Doubtless you know of the significance of SW
winds in spring for migration. But appreciating the
difference between the two principal means by
which SW winds are generated in Ohio can mean
a more rewarding day in the field. Today much of the
state of Ohio has been under the influence of weather
generated through Amplified Flow as opposed to the
dominant Zonal Flow in our region. Amplified Flows
involve weather originating from the deep south-
southwest whereas Zonal Flow is the typical West-
East drift of weather across the state. That is an
oversimplification but you already know what I'm talking
about if you have ever been out birding a spring morning
during precipitation which has a warmth to it
that you don't associate with a typical cold frontal
passage. This warm-wet spring birding I noticed
as a teenager at the Shaker Lakes, and soon
identified this weather with causing the best songbird
fallouts most especially of neotropical migrants.
The greatest diversity of warblers I recorded in a
steady warm drizzle, and for years never saw another
birder out in that weather.
The southern origin of this air mass means tropical
moisture is drawn up from the Gulf and rides a
frontal boundary well into the northeast. In a frontal
system from the west or northwest, cyclonic
winds associated with a low pressure center
bring SW winds ahead of the front, switching dramatically
to the W or NW as the frontal boundary passes.
Temperatures are often dramatically higher ahead
of zonal flow as the SW wind is dry, but as today
demonstrated mild temperatures are possible
even in the context of drizzly conditions - this
is not uncommon of Amplified Flow.
So why should you care? I have made a business,
literally, of standing on the shoreline of various
Great Lakes since 1984, simply to count
migrants as they are migrating - as opposed to
staging. Inevitably one becomes curious about
the predictability or non-predictability of
both passage events and fallouts. Zonal Flow
as it influences bird movements is relatively
straightforward. Saturday's hawk flight and
songbird (diurnal) flight was easily predicted and would
have been of no surprise to many a veteran
observer of hawks along Lake Erie. The
afternoon shorebird staging was no less
predictable, as staging builds to its maximum
immediately before the passage of a cold front
(most usually depart the next morning). I was
only surprised by the numbers as the buildup
must have been going on for a week or so
yet no concentrations had been reported
in recent weeks anywhere in the area.
But what of Amplified Flow. I still have to test
out the predictions with this type of flow; the
type of weather I feel is most influential on
whether we see songbird (nocturnal) fallouts.
I normally leave it to myself to be the guinea-pig
for these tests - certainly saving any embarrassment
when I get it wrong - but I thought I'd give it
more public airing. So here goes.
A noticeable increase in localized populations of
migrant songbirds should be noted early tomorrow
morning principally in southern Ohio in a line
extending roughly from Butler County through
Columbus to Canton and Youngstown. Should
be heavier from Columbus west than in eastern
Ohio. Southernmost third of Ohio should see
the arrival of several new early neotropical
migrant warblers on territory plus the widespread
territoriality of the Lousiana Waterthrush. The
other nocturnals I suspect are heavily influenced
by Amplified Flow are the shorebirds and terns.
Watch for a sharp increase in Pectoral Sandpiper
numbers at central and southwest locations
and a few Common Terns at area reservoirs.
I would be checking fields for a flock of American
Golden-Plover, Chimney Swifts over water, and
Whip-poor-wills calling in the environs of the Wayne
N.F. Rails are another great benefactor. Spring
Valley W.A. would be an interesting place to be.
Northern Ohio (east of Sandusky Bay) will be
limited to a nominal fallout within 5 miles of Lake
Erie. Local migrant traps (e.g. Gordon Park,
Headlands Beach State Park) could see notable
concentrations of sparrow species including
juncos but remain weak on neotropicals. Sorry
Toledo your turn comes with the weekend.
All this depends on the weather of course, and
so ultimately I am dependent on the weatherman.
Should the winds shift to the west earlier than
predicted during the night the further west and
south the fallout center should be. Complicating
matters (and possibly enhancing the experience)
is a Zonal Flow cold front immediately on the
heels of this Amplified Flow. I really don't
know what to expect here but my guess is that
the birding experience before mid-morning will
be very different from late morning - meaning
fallout birds, either warblers or sparrows, may
be on the move early so observation is best
done by 10:00 am. The terns especially can
clear out quickly or otherwise be found resting
on a dock amongst gulls rather then conpicuously
flying about.
Later in the week, the weather map shows a
massive warmup with a classic spring high
dominating Thursday - watch for hawks but
best for shorebirds. Friday, just before the
cold front, better for hawks, may see shorebirds
on the wing in the Western Basin. Good diurnal
songbird flight both days but better Friday -
expect pipits in the hundreds.
Well if nothing else - you'll get a good chuckle
when none of this pans out.
Vic Fazio
Shaker Hts., OH
To: ohio-birds@envirolink.org
From: Victor Fazio III
Subject: Amplified Migration