Sighting Record for Utah

Common name:	Chimney Swift
Scientific name:	Chaetura pelagica
Date:	27 May 2019
Time:	7:50 PM
Length of time observed:	29 minutes
Number:	1
Age:	adult
Sex:	unknown
Location:	US 40 bridge over the Green River, Jensen, Utah
County:	Uintah
Latilong:
Elevation:
Distance to bird:	Closest it came was about 100 feet
Optical equipment:	Eagle Optics 8x42 binoculars
Weather:	overcast
Light Conditions:	Bird was mostly backlit against gray sky. Daylight was starting to fade a bit by the end of the observation.
Description: Size of bird:	A little larger than the Violet-green and Cliff Swallows it was with
(Description:) Basic Shape:	Body cigar-shaped, wings scimitar-shaped
(Description:) Overall Pattern:	Dark brown, with contrastingly pale throat
(Description:) Bill Type:	Tiny, almost unnoticeable
(Description:) Field Marks and Identifying Characteristics:	I instantly identified the bird as a Chaetura swift by its stiff-winged flight, cigar-shaped body, and overall dark coloration. But in the field I had no idea whether I was looking at Vaux's or Chimney. The bird was silent. I spent nearly half an hour working to get as many photographs as possible, because I knew this was a good record either way. After studying online resources, I started to lean toward Chimney Swift given the long wings and the bulging inner primaries. I asked for a few opinions. Tony Leukering said, "I d go with CHSW, due to the ss bulge and the apparent lack of a paler rump. However, I m not all that comfortable with Chaetura." Steve Mlodinow added, "I agree with Tony, looks much like a Chimney Swift. For the points Tony makes and this bird has the lankier jizz of a CHSW rather than the stubby feel of Vaux's." I will add that three days after seeing this bird, I was in Oregon and got to study Vaux's Swift, and it quickly struck me as a much fast er-flapping bird than the one I'd seen in Utah, with shorter and straighter-edged wings. For all these reasons, I am now comfortable calling the Utah bird a Chimney Swift. (see photos)
Song or call & method of delivery:	Bird was silent.
Behavior:	Bird was observed only in fast, zooming flight, chasing insects in the air with a flock of swallows.
Habitat:	Air over the Green River and adjacent fields and houses.
Similar species and how were they eliminated:	Vaux's Swift is the species to eliminate. It was ruled out by the longer wings; the slightly bulging inner primaries creating a slightly paddle-shaped rather than straight-edged wing; the dark rump nearly concolorous with the back; and the slower flapping flight (vs. the Vaux's I studied in Oregon three days later).
Previous experience with this & similar species:	I've seen Chimney and Vaux's many times, but never spent any time learning the fine points of distinguishing them, until after this encounter.
References consulted:	"Identifying Chimney and Vaux's Swift by wing shape" by David Sibley (sibleyguides.com) and "Identification Summary of Vaux's and Chimney Swifts" by Andy Birch (surfbirds.com). Also expert opinion from Tony Leukering and Steve Mlodinow.
Description from:	From memory From photo(s) taken at the time of the sighting
Observer:	Nathan Pieplow
Observer's address:	5902 Gunbarrel Ave Apt C, Boulder, CO 80301
Observer's e-mail address:	**
Other observers who independently identified this bird:	none
Date prepared:	31 May 2019
Additional material:	Photos [eBird]
Additional comments:	I have more photos of the bird if necessary, though the best ones for showing wing shape and rump color are included here.