Before ice locks up inland lakes and ponds, Common Loons head to the open ocean where they attempt to ride out the white season. Though they no longer sport their familiar black-and-white breeding attire, their large size helps them to stand out among other wintering waterfowl. Two smaller, less-common loons occur along the New England coast in winter: Red-throated Loon and Pacific Loon. White-season Common Loons have heavy, gray bills, scalloped gray backs, dark crowns often appearing flattened, and a jagged collar. They largely feed on fish, though I've seen individuals feeding on crabs, too. (To view the following images in full-size, click here.)
Lastly, here's a brief Common Loon video meditation.