Hi Tom,

Every year I try to figure out a better way to estimate the number of
nocturnal migrants flying over my Battle Ground, Clark County yard and I
basically learn nothing new every year.

I go back and forth trying to figure out if one can hear an individual
thrush 2 or 3 times as it passes over. I've even gone to the local refuge
where it is quiet and had a friend walk 100 hundred yards away and play a
recording of an "*urp*" to determine how far away you can hear it. Listen
to the recording and then determine the amount of time between each "*urp*".
Take that distance and apply a speed of flight and, in theory, you can
figure out whether it's 2 or 3. Never knew I would be using math this way!

The Swainson's Thrushes were flowing nicely last night and early this
morning over my Battle Ground, Clark County yard. As usual, activity
seemed to peak at around 5:30am. I counted the number of "urps" over a 1
minute period 5 times and I heard between 15-35 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 5-12 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.) Do birds call more frequently closer to dawn or when they are at lower
flight elevation?
6.) Are different flocks flying at different altitudes - some within
hearing range and others not?
7.) Do birds vocalize more when flying through smoke .... or less?
8.) Do they call more ... or less ... when encountering a headwind?

etc.

I have no idea about Savannah Sparrows but I think that during the day,
they seem to call slightly more frequently than Swainson's Thrushes when
flying overhead during the day. I might be wrong on that though.

Continued clueless in Battle Ground.

Keep your eyes and ears skyward.

Jim
Battle Ground, Clark County, WA

On Wed, Sep 16, 2020 at 11:09 PM Tom Benedict <benedict.t at comcast.net>
wrote:


> I'm interested in how one identifies and counts nocturnal migrants. Can

> you hear them calling? Must be flying at relatively low altitude.

>

> Thanks for further details.

>

> Tom Benedict

>

> > On Sep 16, 2020, at 22:46, Isaiah n <isaiahn0919 at gmail.com> wrote:

> >

> > So far in the last hour I've counted 540 nocturnal migrant Savannah

> Sparrows flying over my yard in southeast Bellingham and they continue to

> be flying over constantly! Also good numbers of Swainson's Thrushes and a

> few American Pipits.

> >

> > Good birding,

> > Isaiah Nugent

> >

>

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