"mystery bird"

The second picture in my August 9th post appeared to be of a very strange bird -- some of you wrote asking what it was.
It all started when I was photographing White Pelicans near the dam at the south end of Big Stone Refuge.

There among the rocks was this "ratty" looking Great Blue Heron. It stood motionless for about an hour as I was busy taking photos of the Pelicans. I was wondering whether it was ill? -- its feathers were in such disarray -- could it have been in some oil slick?

When I returned about a half-hour later, there it was peering at me from the other side of the dam. It must have been physically able to fly over a distance of some 100 feet.

After gazing at me while I was taking pictures of Pelicans & Cormorants, it crouched down, laying almost flat on the rocks.

I certainly wasn't going to approach it or bother it -- yet I was concerned about its welfare. Another hour or so passed and I had to leave the site. Looking at the pictures, does anyone have an idea what may have been the matter with it?