Yesterday I stopped at Fishing Rock State Park. 44.846101,-124.052222
I looked down on 2 Ruddy Turnstones foraging in the intertidal zone. This is a species I don't see every year. Sometimes I pick up a bird at the port dock in Bandon at the Shorebird Festival in the fall, sometimes not. I'm usually just happy to see one.
What struck me about these two birds in spring breeding plumage was that they were DIFFERENT. One had brighter chestnut patches on the wing and back, and the head was WHITE WITH FINE BLACK LINES, while the other had BROWN ON THE CROWN AND NAPE, and the wings were duller chestnut. I figured they were a male and female, but I'd never seen this in 40 years of birding. Back at the car I looked in Sibley's and National Geographic guides and found only the breeding male illustrated. Luckily I had Dennis Paulson's Shorebirds of the Pacific Northwest along and it showed the difference I had seen. It was indeed a difference between the sexes.
Back home, I just looked through these guides and found they ALL showed only breeding males, not breeding females:
Sibleys, National Geographic, Robbins, Stokes, Peterson's, Audubon's (photographic), Am Bird Conservancy, Audubon Master Guide to Birding
The only common guide that shows the breeding plumage female is (drum roll) Kaufman's Focus Guide.
Of course, Paulson's guide and Shorebirds by Hayman, Marchant, and Prater go into more detail than the common general-purpose guides. These references show the breeding female with her brown cap and nape.