Other Observers: Missy Arnold, see our eBird entry of 12 Jan 2017:
Pat Weber found it on the following day and obtained video, see her eBird entry of 13 Jan:
LOCALITY OF OBSERVATION
In Twin Falls County at Upper Salmon Power Plant A on the Snake River (eBird hotspot). Benchmark Atlas pg 73, grid 10:G
HABITAT WHERE THE BIRD WAS OBSERVED
Open water below power plant. Hagerman Valley hosts numerous hot springs, providing the Snake River with warm water above ambient temperatures in winter, thereby attracting many waterfowl and other species that might not otherwise be there in January. A wide variety of native and introduced shrubs and trees line the margins of ponds and streams/rivers thereabouts, providing extensive shelter for wildlife, and there are contiguous areas of agriculture. Human population density in the area is low.
SIGHTING DURATION, CONDITIONS, and EQUIPMENT USED
17F, mostly sunny, calm to light breeze, no ambient noise other than moving water at the power plant.
DID YOU TAKE NOTES?
Yes, during the observation
DID YOU CONSULT A FIELD GUIDE OR OTHER REFERENCE WORK?
Yes, during the observation
WHICH GUIDE(S) OR REFERENCE(S): DID YOU CONSULT?
We carry several field guides with us on our road trips, but usually check Sibley first. We also carry eBird bar graphs illustrating the seasonal occurrence of birds in Idaho… valuable information to have at hand because we could see that this species isn’t expected in Idaho until late Feb or early March.
DESCRIPTION OF THE BIRD(s)
First looks at this bird were when it crossed thru my field of view while scoping waterfowl below the power plant. It was a swallow foraging above the water, darkish above, very white below, could not make out extensive white flanks (sides of rump) that VGSW shows from above or when the bird banks in a turn.
BEHAVIOR OF THE BIRD(s)
Bird was foraging above open water the whole time we watched it; flight not as buoyant or gliding as BARS appears to us; didn’t leave the area or stop foraging while we watched.
HOW AND WHEN DID YOU POSITIVELY IDENTIFY THE BIRD, AND WHAT CLINCHED THE IDENTIFICATION FOR YOU?
Bird wasn’t just crossing the water like a shorebird usually would, but was flying back and forth and circling, very near the water surface, obviously foraging. We knew this was a swallow, but we weren’t seeing the colorful markings, long tail, nor flight pattern of a BARS. Missy noticed a bluish hue on the bird’s back, and re-emphasized how white the underside of the bird looked, i.e., not a NRWS, etc.
HOW DID YOU ELIMINATE SIMILAR SPECIES? WHAT WERE THEY?
To our eyes, TRES can be confused with VGSW if not carefully noting the sides of the rump when seen from above. Our other typical swallow species do not look dark above, pure white below, and/or look drabby or have apparent field marks to set them apart. Admittedly, a Blue-and-white Swallow (Central and South America) in flight would look quite similar to TRES.
WHAT IS YOUR EXPERIENCE WITH THIS (AND SIMILAR) SPECIES?
I’ve observed 23 sp of swallows in the Western Hemisphere during the last 20+ years, and I’ve seen the typical U.S. species annually, with recent exceptions of PUMA and CASW.
DESCRIBE YOUR GENERAL BIRDING EXPERIENCE
Passive interest in the 70’s (Mexico and UK); focus on hummingbirds in the 80’s (western US); broadening interest in the 90’s (mainland US, Alaska, British Columbia, Europe); active interest in birds of Central and South America beginning in 2005 (19 birding trips to 12 countries).
ADDITIONAL INFORMATION (If any)
[Observation occurred on] 12 Jan 2017, [at] 1110 hrs
Were photo(s), video, and/or audio obtained? Not by us, but please see Pat’s video if available.
Description supports the identification of Tree Swallow.
could not see the video - description is convincing.
Reject, specific identification not established
I would like to see some additional discussion on this record and especially, if available, the purported video. I'm not convinced N. Rough-winged Swallow is eliminated from that description and if I'm not mistaken that species has been documented previously in December along this stretch of the Snake R. In addition, Tree Swallow appears to be quite rare in winter in the inter-mountain West.
Description of behavior and basic field marks sufficient, including separation from Violet-green Swallow. Tree Swallow also most likely to over winter in Idaho.
Bird was well described and description eliminates similar species
SECOND ROUND VOTING:
Charles’ point about the potential of No. Rough-winged Swallow (Stelgidopteryx serripennis) is a good one. However, the observer’s mention of the bright white underparts sharply contrasting with dark upperparts points to the original identification. I’m going to continue with my “accept” vote.
no change from round 1 vote
still convinced that it is a Tree Swallow
I'm still comfortable accepting this record.
same comments as before
Would still like to see the video but I guess this is sufficient. I'm not sure the data support Tree Swallow being the most likely winter swallow (and any swallow still seems quite rare Dec-Jan) in Idaho but will be interesting to see if this changes with climate.