Andrew,
I like your investigative approach.
Right now the primary evidence suggesting the characteristics of Bicknell's
thrush flight call is still tentative and based largely on the
distinctiveness of "Gray-cheeked" type flight calls recorded in east-central
Florida during spring migration -- a time and place where Bicknell's is
thought to be the more frequent & consistent "Gray-cheeked".
From what I've seen in my collection of presumed eastern Florida Bicknell's
flight calls, your call is not from Bicknell's but fits in the typical
Gray-cheeked (C. m. aliciae) category. Looking at your spectrogram, if you
are measuring a high frequency point at over 4.5 kHz you are using the upper
edge of the time-frequency contour as your measuring point and this high
point is near the center of the length of the call. You'll note in my paper
on Bicknell's nfc (Table 1) that the MN birds had a mid-point mean high
frequency of 4.2 kHz with a .18 standard deviation - and this data was
measured from the middle of the time-frequency contour (not upper edge). So
this evidence suggests it is not uncommon for C. m. aliciae to reach 4.5, or
a bit above, near its mid-point. Also, keep in mind that the frequency of
Gray-cheeked calls may vary perhaps +/-100 Hz depending on whether the bird
is recorded on approach or flying away from a recording station (Doppler
shift).
The evidence from Florida also suggests that you will not find the high
point of a Bicknell's flight call at its mid-point, but rather near the
beginning. The catch here is that it appears some Gray-cheeked calls have
their high point near the beginning of the call ...so there may be overlap
between high Gray-cheekeds and low Bicknell's in this regard.
Still lots to learn here but your call suggests Gray-cheeked and not
Bicknell's to me.
Bill E
p.s. Perhaps worth noting that some taxonomists believe there is another
small subspecies of Gray-cheeked up there somewhere.
----- Original Message -----
From: "Andrew Albright" <andrew.albri...@gmail.com>
To: "nfc-l" <nfc-l@cornell.edu>
Sent: Monday, September 19, 2011 11:13 PM
Subject: [nfc-l] Gray-Cheeked or Bicknell's Thrush?
Early this morning, I recorded a nfc that's seems in between
Gray-Cheeked or Bicknell's Thrush. I checked through the archives of
this list and this topic doesn't seem to have been discussed to death.
BAYESIAN INFERENCE
With several days of nice Northeast winds, I figured that Bicknell's
Thrush was possible to record in southeastern PA. Pennsylvania doesn't
have any ebird records of Bicknell's but New Jersey and Maryland seem
to be all in early October. Wilson and Watts, 1997 show that
Bicknell's is possible in the general area, but unlikely on Sept 19th.
Same with Birds of Pennsylvania with banding records starting on
Sept 20th.
SONAGRAM ANALYSIS
Gray-cheeked Thrush is much more common in general and on September 19th.
The main sonagram of interest peaks over 4.5 kHz and nothing I can
find for Gray-cheeked are much more than 4.0 kHz.
Shape - seems to suggest Bicknell's from most published recordings
(except for the nocturnal page on the nfc CD)
In the second set of sonagrams, I made a composite of 4 nfcs
1) A nfc that looks like Gray-Cheeked Thrush, especially if I increase
the "y" axis of time.
2) The main sonagram of interest (shown above).
3) This call was right after the possible Bicknell's and I didn't cut
it out. It was weak but sounded like a Swainson's and maybe looks
more like Wood Thrush.
4) Lastly is another higher pitched call that's seems like it may be
Gray-cheeked (except for the "M" shape).
EAR ANALYSIS
Listening to the nfc CD's recordings of Bicknell's and Gray-Cheeked
has me leaning toward Bicknell's. But this is pretty subjective and
maybe only because of the higher pitched recording.
Sincerely,
Andrew Albright
Maple Glen, PA
Weblinks to sonagrams of Gray-Cheeked and/or Bicknell's
http://www.birds.cornell.edu/birdcalls/species/Thrushes/Gray-cheeked%20Thrush%20%28Catharus%20minimus%29/
http://www.nightmigrants.com/main/page_species_calls_graycheeked_thrush.html
http://pjdeye.blogspot.com/2009/02/thrush-calls.html (Recording of
Bicknell's in S.E. Pennsylvania)
--
NFC-L List Info:
http://www.NortheastBirding.com/NFC_WELCOME
http://www.NortheastBirding.com/NFC_RULES
http://www.NortheastBirding.com/NFC-L_SubscribeConfigurationLeave.htm
ARCHIVES:
1) http://www.mail-archive.com/nfc-l@cornell.edu/maillist.html
2) http://www.surfbirds.com/birdingmail/Group/NFC-L
3) http://birdingonthe.net/mailinglists/NFCL.html
Please submit your observations to eBird:
http://ebird.org/content/ebird/
--
--
NFC-L List Info:
http://www.NortheastBirding.com/NFC_WELCOME
http://www.NortheastBirding.com/NFC_RULES
http://www.NortheastBirding.com/NFC-L_SubscribeConfigurationLeave.htm
ARCHIVES:
1) http://www.mail-archive.com/nfc-l@cornell.edu/maillist.html
2) http://www.surfbirds.com/birdingmail/Group/NFC-L
3) http://birdingonthe.net/mailinglists/NFCL.html
Please submit your observations to eBird:
http://ebird.org/content/ebird/
--
