Most birds have 10 primaries, numbered 1 through 10, therefore P1, P2, etc
starting closest to the body. Note that P10 on Catharus thrushes is vestigial,
barely visible. Counting down, 10,9,8...note that the leading edge of of P6 is
not even thickness all the way to the tip. It abruptly constricts halfway to
the tip and this is the "emargination". SWTH have a straight, ie unemarginated
P6 and l learned yesterday that Gray-cheeked Thrushes are similar. As for
"P9<P6" that means P9 is shorter than P6. I haven't been present when this was
applied in conjunction with banding, but it's a useful concept across taxa.
Think of the Gyrfalcon where P8>P10. That gives the open wing a rounded look at
the tip. In Peregrines P10 is longer than other primaries, or at least P9=P10.
A picture taken with a mobile phone might reveal this detail. I never have any
luck with my own eyes in real time on any such clue from the moving wings. I
believe a similar difference exists between Bald and Golden Eagles. I first
encountered this primary differential as an ID tool in a British field guide in
the 70s, applied to leaf and reed warblers. Hardly a field mark, but a reminder
of the limits to field ID. There's the almost inevitable splitting of
Hermit Thrush into three full species. That will really create some fun. Bob
Archer posted links not long ago to detailed articles on Catharus ID. It popped
up when l was rather busy but look forward to careful perusal when winter
really sets in. The visual difference between various taxa of Hermit Thrush can
be at least as big as the difference between it and other Catharus already
accorded full species.Sent from my Verizon, Samsung Galaxy smartphone
-------- Original message --------From: "Paul T. Sullivan"
<paultsullivan@xxxxxxxxxxxx> Date: 12/15/21 9:42 PM (GMT-08:00) To: OBOL
<obol@xxxxxxxxxxxxx> Subject: [obol] Re: Catharus thrushes Between these two
emails (below) there must have been a bunch of information shared. It didn’t
appear here on OBOL. So let me ask: Since when is tail color NOT definitive in
distinguishing Hermit Thrush from other thrushes???? If not that, then what?
We’ve had discussions about winter putative Swainson’s Thrushes in the past,
and I still have not seen a clear exposition of the story. I believe it
involves subspecies of each species, but I’ve never seen it laid out clearly.
For example:Hermit thrushes have (say 4) subspecies1234 Swainson’s thrushes
have (say 3) subspecies123 And subspecies #2 of Swainson’s Thrush looks almost
the same as subspecies #3 of Hermit Thrush. Paul Sullivan OregonDate: 12/15
5:15 PMFrom: Christine Maack <cmaackster...>Subject: [obol] Catharus
thrushesThanks for all the information about hermit thrushes in Oregon. Now
that Ican't use tail color as definitive, what are good ways to
distinguishbetween hermit and Swainsons (in season)?ChrisOregonDate: 12/14
12:30 PMFrom: Christine Maack <cmaackster...>Subject: [obol] Mystery thrushGot
a good look at a catharus thrush under someone's feeder this morning.Did not
have any rufous in the tail and had pale legs. Could have been aSwainson's or a
Gray-cheeked. Which is more likely?Chris
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