Twin Falls County, between Filer and Twin Falls cities, along 2500 E, specifically in the vicinity of 42.543102, -114.556763.
HABITAT WHERE THE BIRD WAS OBSERVED
Rural-urban area with somewhat equal mixes of tall trees, housing, farm fields.
SIGHTING DURATION, CONDITIONS, and EQUIPMENT USED
I observed the bird for about 5 minutes, plenty of time to see field marks and get a good idea of identification. It was early in the warm afternoon, minimal cloud cover, bright sun provided good lighting with the direction of the bird coming from the north. I observed the bird well with Vortex 10x42 binoculars and took photos with Nikon Coolpix L820.
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?
National Geographic 6th ed. (2011); Sibley Guide to Birds of North America 2nd ed. (2014)
DESCRIPTION OF THE BIRD(s)
The bird was clearly a hawk, my notes and memory indicate about the size of a big female Cooper's Hawk. The flight pattern I observed was several solid flaps followed by a short glide, also reminiscing accipters, to which this bird is similar to. The bird initially flew towards me head-on but then turned sideways, where I saw the solid brown head, brown streaking below (which was rather heavy suggesting elegans ssp), rufous wing linings (pointing to elegans ssp), bold wing crescent at base of primaries (it was particularly bold on the upperwing also suggesting elegans ssp), black tipped primaries, white scalloping on the rump, and thinly banded tail. The bird also lacked a whitish rump, further suggesting the Pacific ssp, elegans.
BEHAVIOR OF THE BIRD(s)
The bird was initially seen flying towards me head-on from about 150 meters to the north. It flew to the top of a lone pair of leafy trees, where it stayed for about 30 seconds. It then flew east about 100 yards to the top of a section of cottonwoods, this flight is where I took most of the pictures and it. It stayed there a little less than a minute, from where it flew south and slightly west out of sight, which was about 400 meters into an area with many taller trees. Throughout this observation the hawk was being mobbed by Western Kingbirds and American Kestrels.
HOW AND WHEN DID YOU POSITIVELY IDENTIFY THE BIRD, AND WHAT CLINCHED THE IDENTIFICATION FOR YOU?
As soon as I put binoculars on the bird I knew it was different. The general size and mottling brought me to think young Red-shouldered or Broad-winged Hawk. However, the reddish underwing coverts, solid dark brown head, scalloped upperparts, thinly banded tail, and white-wing crescents at base of primaries all served to quickly point me to Red-shouldered, specifically the Pacific ssp. elegans).
HOW DID YOU ELIMINATE SIMILAR SPECIES? WHAT WERE THEY?
Any larger accipiter species, namely Cooper's Hawk or Northern Goshawk, were readily eliminated by mottling pattern on underparts and reddish underwing coverts. The most similar species was Broad-winged Hawk. It was readily eliminated by lack of black trailing edge on wing, thinly banded tail (not broad tail bands), scalloped mottling on upperparts (Broad-winged has pretty solidly brown upperparts), and white crescent at base of primaries.
WHAT IS YOUR EXPERIENCE WITH THIS (AND SIMILAR) SPECIES?
I have extensive experience with the expected hawk and falcon species of Idaho and some experience with Red-shouldered Hawks, having observed them near coastal Oregon about 15 years ago and summer of 2018 in far eastern Kansas.
DESCRIBE YOUR GENERAL BIRDING EXPERIENCE
Extensive, been seriously birding most of the my life (~14 years) with the most intensive birding the last 10 years and most of my time in southern Idaho.