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The post below just came in from the Oklahoma list. It provides a meteorological explanation for fallouts of southwestern Cave Swallows in the northeast at this time of year.

Bob Fisher
Independence, Missouri
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----- Original Message ----- 
From: Victor Fazio 
To: [log in to unmask] 
Sent: Monday, November 14, 2005 7:41 PM
Subject: Re: Cave swallows on the great lakes.


For 6-7 years, the passage of an powerful cyclonic storm with deep
low pressure, whereby that low center passes from the SW to the NE
in a relatively rapid fashion, in conjunction with excessive warmth
due to strong SW winds ahead of the ssytem, has produced massive
fallouts of Cave Swallows throughout the NE. These are highly
predictable events having consistently taking place from the last
few days of October through mid-Nov. Initially, only a single cylconic
event produced Cave Swallows. However, last year, and this year,
there has been a strong initial event followed by an echo flight.
The strength of the fallout varies year-to-year, though there seems
to be an upward trend (this past 10 days has seen 600 birds into the
southern Great Lakes, however this may be partly due to an offset 
to the fallout as the east coast did not fair as well as previous years).
Indeed, the half-dozen OH sightings, involving perhaps 50 birds, are
that state's first records, having missed out by just a few miles in
past events.

We are still learning the basic nature of this event. However,
extrapolating from similar events involving species migrating at this
time, it would seem that 

1. one or more populations of Cave Swallow,
2. possibly staging en masse
3. disperse/migrate around 1 Nov (+/- a week)
4. and should a powerful cyclonic force coincide with this
5. a substantial number of these birds are brought NE
6. and dumped out at the point where the low often dissipates
7. either off the central Atlantic coast in a more southerly track
8. or the southern Great Lakes in a more northerly track

there are a few assumptions there and this is little more than 
my best guess from plotting the fallouts against the various
storm tracks with some attention to where isoclines broaden
indicating a dissipation of winds. The fallout, in a fashion 
reminiscient of that involving hurricane borne birds, as well 
as a striking fallout event in Oct 1998 whereby 400 Franklin's
Gulls appeared across western Ohio (2000 birds across the
Midwest), these swallows 

1. appear in front (ENE) of the storm passage
2. as the storm enters the area.

subsequent sightings are few, with no more 5% detected lingering
at any given site. In other words there is almost no chasing of these
birds ... you have to be there on a shoreline to watch the passage
of bird as the low pressure system bears down on your position.

As to why we are seeing this now. Certainly the burgeoning
populations of the Cave Swallow and their gradual movement
northwards is involved somehow. Also there is the matter of these 
powerful cyclonic events coming out of the SW (I often can draw a
line from roughly the panhandle of TX to Dallas as a starting point).
Are they more frequent? More powerful? Last fall, I commented 
in my North American Birds column covering OH-PA-WV that the
latter half of the fall period was dominated by these events with only
a single typical storm out of the NW in mid-Nov. I also speculated
on the remarkable number of potential reverse migrants noted that 
Nov (see Table in North American Birds) which culminated in the
December appearance of a Chuck-will's Widow near Cincinnati.

Again, a lot of speculation. How birds, not as individuals, but as
populations react to large scale weather events during migration
is something which has seen little attention away from the Gulf
Coast. Furthermore, our data sets are rathered muddled by the fact
that few birders are out and about in the thick of inclement
weather. At various Great Lakes promitories, a small dedicated 
cadre of slightly insane souls have been making a point of standing 
on some exposed jetty or  sand spit in the face of a biting Nov 
wind for 30-40 years or so, although this activity has really picked up
in the last 15 years. Patterns are emerging, while new 
events, perhaps overlooked by virtue of their discrete nature, are
coming to light. 

In short, we live in very interesting ornithological times, where 
technology, communications, travel access come together to
allow monitoring what I call event birding. For example, a few
years ago I was monitoring an intense storm moving across 
the midwest that was going to involved the entire state of Ohio.
It was mid-March and an ice front was apparent to Doppler radar.
Given the coincident timing with the anticipated arrival of
Horned Grebe coupled with anecdotal evidence of that species'
susceptibility to grounding in the wake of ice-storms, I alerted 
the Ohio birding community via listserv to a potential fallout and urged a
survey of water bodies along the edge of the storm. The 2000
grebes censused was among the largest spring fallouts on 
record for the state.

There are more gaps in our knowledge of these discrete events
than substance. And much of that substance is in flux as is 
seemingly our weather and may require a new interpretation.
Bottomline, no birder anywhere should assume we KNOW all
that much about bird distribution, let alone why it is so, and 
I encourage a continued participation in the ornitholgical
record through careful note-taking and perhaps a little consideration 
for the weather.

cheers

Vic Fazio
Shaker Hts., OH
http://aves.net/



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