Yesteday at Tri-Town I had a loon that was of interest. I had a brief look at it before it dove and I could not relocate it. I am familiar with common and red-throated loons but this loon struck me as different. It had a dark back, a distinct contrast with the border on the neck. I thought I may have seen a chin strap. Bill didn't seem to be as robust as a common. Unfortunately the common loons that were there were not in close proximity with this bird so I could not compare size.