I thought this was a Bufflehead Duck, but thanks to Michelle Sixta who assists with identifying birds at whatbird.com, this is actually a Smew. Michelle told me that "Sometimes birds have different plumage depending on the stage of their development and even the time of year, so it can be tricky. The Bufflehead pretty much looks the same all year round and has distinct patches of black and white, e.g., white patch on the top/back part of its head and an all-white breast. Whereas the Smew has some of its own distinct patterns like the black lines descending down the front of the breast and the black eye patch." Thanks, Michelle, for your help.