During the several days following the my initial observation, myself, Kimberli Conrad, Sarah Harris, Ken Harris, Charlotte Eberlein, and Stoddard Davenport were able to see the bird.
LOCALITY OF OBSERVATION
The bird was seen barely west of the main parking lot at Auger Falls Basin trails in Twin Falls County. This area lies in the Snake River Canyon beside the Snake River. The observation was specifically at: 42.621332, -114.512865.
HABITAT WHERE THE BIRD WAS OBSERVED
Scrubby habitat with Russian Olive and woody shrub overstory with cheatgrass and rabbitbrush understory. A fire went through the area about 10 years ago so the area was laiden with dead trees/snags as well.
SIGHTING DURATION, CONDITIONS, and EQUIPMENT USED
I observed the bird at dusk on 31 Dec. 2017 as it flushed from the ground several feet away into a Russian Olive about 15 feet away. I put my 10x42 Vortex Diamondback binocs on it and observed it for a good 35 seconds. It was a mostly clear day with chilly temperatures and no wind at dusk.
DID YOU TAKE NOTES?
Yes, later the same day
DID YOU CONSULT A FIELD GUIDE OR OTHER REFERENCE WORK?
Yes, later the same day
WHICH GUIDE(S) OR REFERENCE(S): DID YOU CONSULT?
The Sibley Guide to Birds of North America iphone application.
DESCRIPTION OF THE BIRD(s)
When the bird flushed into the olive, I I quickly noticed grey underparts, brown mottled upperparts with two thin wing bars, and thin black supercilium with golden central crown stripe. The bird also sported a bicolored bill. Small, stocky shape combined with short bill, long tail, and medium-length wings express the classic sparrow look.
BEHAVIOR OF THE BIRD(s)
The bird flushed from the ground by itself with no other birds with it, probably foraging, and flew into a nearby Russian Olive. There it began to eat the olive seeds for about 35 seconds. It then flew into the thick understory of the Russian Olives and other woody shrubs, where it called once (a high-pitched downslurred “teew”).
HOW AND WHEN DID YOU POSITIVELY IDENTIFY THE BIRD, AND WHAT CLINCHED THE IDENTIFICATION FOR YOU?
The clear underparts and black and gold crown clinched the ID for me, and the call note given later was the "cherry on top" so to speak.
HOW DID YOU ELIMINATE SIMILAR SPECIES? WHAT WERE THEY?
The similar Zonotrichia species, White-crowned, White-throated, and Harris's Sparrows were readily eliminated bu the clean gray underparts, black supercilium, gold crown, bicolored bill, and "teew" call note.
WHAT IS YOUR EXPERIENCE WITH THIS (AND SIMILAR) SPECIES?
My experience with this species is intermediate. I have observed several individuals of this age in Idaho over the past 8 years (one was seen the week prior to this observation). I have observed the other three Zonotrichia species much more often, almost annually for WTSP and HASP and almost daily for WCSP.
DESCRIBE YOUR GENERAL BIRDING EXPERIENCE
Extensive. I have been avidly birding in the Intermountain West especially for about 8-10 years.
ADDITIONAL INFORMATION (If any)
On 31 December 2017 I was unable to obtain photos so I returned then following morning (1 Jan. 2018) and got photos and foraging video. The video is posted as a link to Flickr.
Also, the bird appeared to have a bill deformity, a wrinkly bulge on the upper mandible.