Date: 3/7/17 12:17 pm
From: Anne & Dan Heyerly <tanager...>
Subject: [obol] Trumpeter v. Tundra Swan ID: The eyes have it!
Obolinks,

With all the variation of yellow/no yellow lores, "U" vs. "V" forehead
feathering when the swan is directly facing you, or is the bill concave or
straight (profile)? The discussion up to this point centers around those
three things, but in my opinion neither is always distinct as a thing. Two
weekends ago Anne and I birded in the Skagit River area north of Seattle,
where a good number of both Tundra and Trumpeter Swans were present. We
came to rely on looking at the eye for identification of these birds.
Trumpeter's broad black connection of the eye and the mask was what we
focused on, or as David Sibley says in a Feb. 19, 2006 article on the Sibley
Guides website
(http://www.sibleyguides.com/2006/02/distinguishing-trumpeter-and-tundra-swa
ns/), "the Trumpeter's eye is broadly connected to the black bill, whereas
the Tundra's eye appears nearly separate from the bill. The Tundra Swan
illustrated is one of the approximately 10% of all adults that show no
yellow on the lores. The separation of eye and bill is even more pronounced
when any yellow is present. On juveniles the feathering is more extensive
than on adults, and therefore this feature is more variable, but probably
still useful. The V-shaped border on the forehead of Trumpeter Swan (vs
U-shaped on Tundra) is useful, but can be hard to judge and some birds
appear intermediate."

To me, another way of looking at this is to think of the appearance of the
Tundra's eye as sort of "pinched off" from the black connecting the eye to
the bill, whereas a Trumpeter's dark eye simply expands directly to the bill
with no "pinching" (". . . broadly connected to the black bill" - D.
Sibley).

Whether the bill is straight or concave, is the forehead feathering a "u" or
a "v", how large is the bird, etc. are all field marks, but all are variable
depending on which way the bird turns its head (except for size of the bird,
which is not wise to rely on unless you are certain both species are present
to compare). It's sort of like relying on the black and white markings on
dowitcher tails. Not 100% reliable! When we found a mix of both in a flock,
which was not a common occurrence, our identifications were confirmed when
they "spoke".

Good Birding,

Dan Heyerly, Eugene


 
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