I'm certainly no shorebird expert, but one thing I've noticed in my field guides is that Mountain Plovers typically have darker lores, even in non-breeding plumage, and I also see the tan color coming all the way around the front of the breast, and this bird seems to have a more pale breast. That all said, I don't know what's within the range of expected plumage for Mountain Plovers.
n/a
n/a
The Black-bellied and Golden-Plovers were the first ones I thought of and eliminated. Those options all seemed a little too large and the spotting patterns of winter plumage. There are no neckbands which eliminated all other plover options
Internet, Stokes Field Guide and Petersen's Guide to Western Birds
Photo © Mike Hearell
Photo © Mike Hearell
Photo © Mike Hearell
Photo © Mike Hearell
Photos © Paul Higgins