Despite seeing triple digit numbers of Red-throated Loons every year, I'd never had a good look at one in breeding (or near-breeding) plumage. This bird appeared off the pier a few days ago (the same day as the Arctic Tern in fact). A few white feathers are starting to appear in the face, and the bird is moulting all of its primaries (it can't actually fly at present). Pyle states that Red-throated Loon does indeed moult all of its flight feathers prior to its pre-basic moult into winter plumage, usually in staging areas away from the breeding grounds.
This is the more traditional look to Red-throated Loons. This bird was actually calling, it sounded more like a Caspian Tern than a Common Loon.
This Common Loon flew past the pier at close range. I'd never noticed the vent strap before.