[Tweeters] Battle Ground Night Flight

Jim Danzenbaker jdanzenbaker at gmail.com
Thu Sep 3 18:59:27 PDT 2015


Tweeters,

The Swainson's Thrushes were flowing nicely last night and early this
morning over my Battle Ground, Clark County yard. Activity seemed to peak
at around 5:30am. I counted # of "urps" over a 1 minute period 5 times and
recorded between 20-50 notes each time. Given a prior year's analysis and
observation, I believe that a single Swainson's Thrush will vocalize up to
3 times within my hearing range. Therefore, the number of birds this
morning varied from (conservatively) about 7-16 birds per minute. This is
well short of the peak of thrush migration when one can hear hundreds of
"urps" per minute. As is the case every year, I end up with more questions
about this impressive migration than I have answers. For example:

1.) How many Swainson's Thrushes are in each presumed flock of nocturnal
migrating birds? Can one figure this out if the "urps" come in groups and
then several minutes of silence?
2.) Do they migrate in flocks like American Robins?
3.) If the answer to question 2 is "yes" then why are there so many calls
within a half hour preceding dawn? It sounds like there is one continuous
flow at this time.
4.) Do all birds call when migrating or is it mostly the adults - or first
year birds....or both?
5.) Are different flocks flying at different altitudes - some within
hearing range and others not?

There were some non-thrush chips thrown in for good measure this morning
too. I'm guessing Black-throated Gray Warblers and definitely several
Yellow Warblers. Daytime observation of both of these warbler species
around my tiny yard this morning gave credibility to that educated
identification guess. I'm currently not recording sonograms so have nothing
to compare the notes to for 100% identification assurance.

I think tonight will be another good night.

Keep your eyes and ears skyward!

Jim
--
Jim Danzenbaker
Battle Ground, WA
360-702-9395
jdanzenbaker at gmail.com
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