Later the same day, Darren Clark observed the scoter. In the following several days, a handful of southern Idaho birders also observed the bird.
LOCALITY OF OBSERVATION
Directly above the American Falls Reservoir dam in Power county. The scoter was easily viewable from the beach between the boat ramp and the dam on the north shore of the reservoir. Specifically, the bird was at: 42.779863, -112.875335
HABITAT WHERE THE BIRD WAS OBSERVED
Deep, open water
SIGHTING DURATION, CONDITIONS, and EQUIPMENT USED
I observed the bird for about 35 minutes using 10x42 binoculars and a 60x spotting scope.
Weather: Sunny, clear skies, cold temperatures, light breeze.
DID YOU TAKE NOTES?
Yes, during the observation
DID YOU CONSULT A FIELD GUIDE OR OTHER REFERENCE WORK?
Yes, another day after the observation
WHICH GUIDE(S) OR REFERENCE(S): DID YOU CONSULT?
National Geographic Field Guide to Birds of North America, 7th edition
DESCRIPTION OF THE BIRD(s)
A relatively large duck. The thick body, neck, and head were classic 'scoter' field marks. The Black Scoter exhibited an all dark blackish-brown body, pale belly, dark and unmarked wings, pale tan cheeks, dark cap and nape, and thick black bill.
BEHAVIOR OF THE BIRD(s)
The Black Scoter was observed in a small flock of scoters (5 Surf and 1 White-winged). It dove several times early during the observation but primarily preened and rested in the flock of scoters. It stayed entirely in the deep water near the dam.
HOW AND WHEN DID YOU POSITIVELY IDENTIFY THE BIRD, AND WHAT CLINCHED THE IDENTIFICATION FOR YOU?
The uniformly dark body combined with pale cheek area and a complete lack of white field marks pointed to Black Scoter.
HOW DID YOU ELIMINATE SIMILAR SPECIES? WHAT WERE THEY?
Many other duck species were eliminated by the larger size and uniform dark coloration. The uniformly dark bill and lack of any white markings on the plumage ruled out Surf and White-winged Scoters. The pale tan cheek area also is pointed away from Surf and White-winged Scoters. Similarly, plumage and range ruled out Stejneger's Scoter.
Common Scoter was primarily ruled out by range but also by subtle plumage and shape characteristics. Black Scoter is much thicker and it showed when the bird was beside Surf Scoters. It was not significantly thinner necked or smaller-bodied as one would expect a Common Scoter to be. Also, the dark on the nape was uniform going down the sides of the neck, pointing to Black Scoter. Female-type Common Scoters generally appear more "dark-capped" because of the tapering off of the dark cap down the nap.
WHAT IS YOUR EXPERIENCE WITH THIS (AND SIMILAR) SPECIES?
Extensive. I have observed Surf, White-winged, and Black Scoters multiple times each and in differing plumages in Idaho and Oregon. I have no field experience with Stejneger's or Common Scoter but I have studied up and watched videos of the birds as best as I can.
DESCRIBE YOUR GENERAL BIRDING EXPERIENCE
Extensive. I have been birding in the intermountain northwest for many years, particularly in Idaho.
WERE PHOTO(S), VIDEO, AND/OR AUDIO OBTAINED FROM THIS SIGHTING?
FIRST ROUND VOTING:
Description and photos support identification of Black Scoter.
Description and photos confirm the identification
The photos provide unrefutable proof that this was a Black Scoter.
Photographs are good.
Excellent write up with diagnostic photos.
Excellent documentation including diagnostic photos, detailed description, and discussion of other species.