The link to this thread from Tweeters must have worked for some people as here is a reply I received from one Tweetster:
Hey Bill et al.:
This is a Western Grebe in normal nonbreeding plumage. A pure Clark's Grebe will have a sharp demarcation between blackish and white above the eye, as well as a diagnostic orange (rather than yellow) bill. As far as I can tell, Clark's is extraordinarily rare in the sound. I have seen roughly 40,000 Westerns in the sound, but have yet to see my first Clark's.
Incidentally, I have noticed a number of people lamenting the apparent loss of Western Grebes from Puget Sound in recent years. I remember rafts of hundreds off Edmonds through the winter as recently as 2006-2007. I didn't keep records, but I recall noticing that they seemed scarcer and scarcer until just a few years ago, when I realized that they were effectively absent in the winter. However, they are still abundant during peak migration times; for example, I estimated 7000+ in dozens of rafts stretching north to south as far as I could see about midway across the sound during an Edmonds-Kingston ferry crossing at the beginning of April this year. I have seen similar numbers at the same time in the last few years, and this seems to jibe with the conventional wisdom that their winter range has shifted southward and that they are now mostly a passage migrant in our area.
Best,
Bob Russell
Mukilteo, WA