I always enjoy photographing preening shorebirds. One reason is that its a good sign that the birds are comfortable with my presence, since they wouldn't risk taking their eyes off me if they weren't. I never want to add extra stress to the birds that I'm watching, which means approaching really slowly while crawling in the sand, as well as leaving in exactly the same way when I'm done. And since the birds are ok with me being around them, I can get images of their normal behavior. Its wonderful to have a window into their lives.
I also like preening shots since you can get more definition in each individual feather when they have them fluffed out a bit. Its easy to see a bird's plumage as the overall pattern. But when they are cleaning the feathers, you can see the shape and detail in each one, and how they all fit together.
Here's a third frame that's pretty similar to the first, but there's a little better light on this angle of its face, and the little western sandpiper has an eye on the scene.