While I was fascinated looking at the intricacies of this nest, the one below appeared to be much farther along, and I wondered if this one is finished, and the bird isn't yet sitting on the nest, it was waiting for its mate to come back with some more material. What I learned is that GBH's come back to the same nests year after year and expand them each time, so maybe this nest is just a first-year nest and the other one is several years old. I suppose you've got to start somewhere.
When I first saw this, I was a little concerned because I thought it was a peace of trash and I felt a bit sorry for him, because he kept dropping it and picking it up again. As the scene unfolded, though, I was quite impressed that he was able to extract the clam from the tightly-closed shell.