Species: Yellow-throated Warbler (Dendroica dominica albilora, or ssp.)
Location: Red Rocks Park, South Burlington, VT
Observer: Scott Morrical
Date/Time: 9/7/08. 2 sightings of apparently the same individual.
1st sighting at 8:45 AM, second sighting at 9:20 AM. Total
observation time ~5 min.
Weather: Overcast, temperature upper 50s F, wind NW 10-20 mph.
Lighting/Optics: 1st sighting-- shaded forest understory, no
backlighting; 2nd sighting-- forest opening with some diffuse
backlighting. All observations made with Zeiss 7x42 binocs.
Habitat: Mixed woods. 1st sighting-- bird in understory, 5-10 ft
above ground, range 10-30 ft from observer. 2nd sighting-- bird in
middle canopy, 20-30 ft above ground, range 30-50 ft from observer.
Behavior: Both sightings?the bird?s movements were somewhat sluggish.
The bird exhibited a distinctive, creeping foraging behavior similar
to a Black-&-white Warbler. No hover gleaning. The bird would creep
along one tree branch then make a short flight or hop to another. The
bird made no vocalizations that I could detect. Although seen in an
area of intense migrant activity, it did not appear to interact
directly with other birds.
Size & Shape: This was a largish warbler, and appeared both
long-tailed and long-billed. It was clearly bigger than nearby
Magnolia, Blackburnian, and Black-throated Blue Warblers that I
observed under similar conditions.
Bill: The bill was entirely dark gray, long, and straight. The bill
was clearly longer than those of Magnolia and Blackburnian Warblers
that I observed under similar conditions.
Legs & Feet: The legs and feet were entirely gray in color.
Face Pattern: Distinctive. The eyes were black. A wedge-shaped
black patch extended from the auriculars through the lores, where it
connected with the base of the bill. A white crescent appeared just
beneath the eye. A diagnostic white patch appeared just behind the
auriculars, to the rear (thick end) of the wedge. The upper edge of
the wedge bisected the eye. There was a clear white supercilium
stripe with no evidence of yellow coloration in the supraloral region
that I could see. The supercilium was bounded above by the edge of
the bird?s gray crown, and below by the upper edge of the black wedge.
Upperparts: The crown, nape, and back were all the same even gray
color, without streaks. Two bold white wingbars appeared on each wing.
Underparts: The bird had a bright yellow throat and upper breast,
with a fairly sharp cutoff between the yellow and white zones on the
breast. The throat was framed on both sides by heavy blackish streaks
that extended down from the lower apex of the black face-wedge. The
blackish streaks continued down each side and onto the flanks. The
base color of the underparts (excluding the throat) was white,
including the belly and undertail coverts. A dull buffy wash appeared
on the flanks, however.
Tail: The tail appeared relatively long in proportion to body size
for a Dendroica warbler. There were large white tailspots, but I
wasn?t able to get the exact formula.
All the field marks of this bird point to Dendrocia dominica, a
species I have previously observed on the breeding grounds in Virginia
and Missouri, on the wintering grounds in Florida, and as a vagrant in
coastal California. The most similar species, Grace?s Warbler of the
southwest and (for the sake of argument) pale, first-fall female
Blackburnian Warblers are easily eliminated by a combination of field
marks including incorrect face patterns, streaked upperparts, smaller
size, and proportionally shorter bills.
Race/Sex/Age: Lack of obvious yellow color on supraloral region
suggests albilora subspecies. A caveat to this is that albilora is
shorter-billed than the nominate race dominica, and I thought that
this individual was decidedly long-billed. So go figure! A probable
albilora, I am calling it. This race is expanding its breeding range
in the northeast and so vagrancy might be expected to increase in
northern New England. As for sex and age, I am tempted to call this
bird a first-fall female, due to the uniformly gray crown (an adult or
male would have blackish highlights on the forehead and crown) and due
to the extent of buffiness on the flanks.
For the record, this was the first Yellow-throated Warbler that I have
seen in Vermont, and it becomes the 301st species on my state
lifelist! My 300th species was the Great Gray Owl in Burlington last
Scott W. Morrical, Ph.D.
Professor of Biochemistry
University of Vermont College of Medicine
Burlington, VT 05405
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