Bryan Gates writes in response to Dennis Paulson:

>Dennis says, about YRWA:

>>This species seems so often to be seen in isolated flocks (as Mike Smith
>>reported; I have yet to see any in my neighborhood) that I wonder if
>>perhaps they *migrate* in flocks, something I hadn't thought was
>>characteristic of any warbler.

<cut>

>As for our other warbler species, group movements do not seem to occur...
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>perhaps 2 or 3 Orange-crowns, Townsends, Black-throated Grays, etc, and
>perhaps a loose association of these species, but always small numbers.

<cut>

Hi, Bryan. You were trolling for responses here, no? I showed this
note of yours to co-worker Dave Robinson and he had an epiphany. He was
stationed at Cape St. James on the south end of the Charlottes in the early
'70s. One night near the end of August during the fog season in either 1971
or 1972 (memory of time fades with time), he remembers there being so many
"Wild Canaries", as the then non-birder Dave called them, grounded by the
fog and flying around low to the ground that he was able to kick them up in
clouds with his feet. Estimate of numbers were in the hundreds. Now that he
has gained some birding skill, he realizes that they were Yellow Warblers.
The warblers disappeared when the fog lifted. I believe that many warbler
species migrate at night in a fairly synchronous and wide front. Where
geography and/or weather dictate, these movements can become concentrated
as must have happened in this case. In support of this theory, following is
a cut from a report on a recent meterological conference having to do with
current atmospheric sounding methods written by a Montreal meteorologist. I
hope you find it interesting. I will explain as many of the obtuse acronyms
as I can paranthetically.
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"Finally, Wilczak presented a very informative (and entertaining)
presentation entitled: "Contamination of Wind Profiler Data by Migrating
Birds". That's right folks, by birds. Winds measured with 915 MHz radar and
with the WPDN (Wind Profiler Data Network) profilers often indicated
non-random errors as large as 15 m/s when compared to simultaneously
measured rawinsonde winds. Characteristically, the errors occur below 4 km;
they are a nocturnal phenomenon; beginning shortly after sunset and ending
before sunrise; the errors almost always have a southerly component in
spring and a northerly one in the fall; and there are sharp increases in
the measured signal power and spectral width. Furthermore, contamination
can occur simultaneously over broad areas, with the errors not being
detected by the quality control software. At times, the whole WPDN
indicated the errors which then looked reasonable to a data assimilation
system because the errors were consistent between the profilers. Such an
example was shown and all of the WPDN data were accepted by the NMC
(National Meteorological Centre in Suitland, Maryland) data assimilation
system. Detailed studies of these errors indicated that they are due to the
profilers' detection of migrating songbirds. Fortunately enough, new QC
(quality control) algorithms based on characteristics of the returned power
spectra are being developed and showing promising results. McLaughlin also
discussed this contamination problem at the White Sands Missile Range. One
of his comments was, and I quote: 'Notably though, some of the most
interesting atmospheric events observed have been biological. Since the
beginning of operations at the APRF in December 1991, many examples of
insect, bird, and bat activity have been seen including thin and thick
layers, migrations, and after-sunset phenomena.' "
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Supporting evidence away from the biological field for night migration of
songbirds. I would wager that many of these birds are warblers.
Investigation of contemporaneous banding station activity would no doubt
allow better determination of species components.

cheers,
Jack



// Jack Bowling jack_bowling at mindlink.bc.ca //
// Prince George, BC //
// CANADA //