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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.

Description:

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.

Conclusions:

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.

Other comments:

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  
March!


-- 
Scott W. Morrical, Ph.D.
Professor of Biochemistry
University of Vermont College of Medicine
Burlington, VT  05405
802-656-8260 (voice)
802-656-8220 (fax)
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