Common Loon

In full breeding plumage, Common Loon is one of our most beautiful birds (see below), although more often than not we see the less-striking winter plumage in Sonoma County (above). Common Loon may be present any time of the year, but mostly a winter resident that becomes more abundant during spring and autumn migration. Numbers begin to pick up in late September with the bulk of the winter population present by early November. Common Loons begin to leave the area around mid-April with most gone by mid-May. A few birds spend the summer here, most often at Bodega Bay. Some birds will be in breeding plumage by late April or early May, but just as many of the birds that overwinter seem to stay in "winter" plumage.

The biggest of the three loons normally seen here--Common Loon, Pacific Loon (Gavia pacifica), and Red-throated Loon (Gavia stellata. Winter loons can be difficult, but the three species are comparatively easy to identify if you can get a good look at them. Often we see loons offshore at great distances bobbing on water or partially obscured from view by waves. Loons frequently dive, which means views can be fleeting, and a loon can resurface at a remarkable distance from where it was last spotted, only to disappear again just as you relocate it. Loon identification is, in fact, a frequent challenge. In my view, the neck pattern is the best tool for separating the three species, but get a feel for the relative size of the birds, their head shapes, differences in bill shapes, and typical head postures (see head silhouettes below), and you're a long way toward telling the birds apart, even at a distance. There are good discussions of the loons in winter plumage in Kenn Kaufman's Advanced Birding (1990) and his Field Guide to Advanced Birding (2011).

In Common Loon, look for a heavy, thick bill, usually held fairly close to the horizontal (Red-throated Loon typically swims with its head tilted up). The top of the head of Common Loon tends to have a flattish look (although ruffled feathers can obscure this, and Red-throated Loon can have a similar "anvil-top" look). In winter plumage, look for a zigzag pattern of light and dark on the neck that gives the neck a notched look (clearly visible in the photo above). In breeding plumage, the notches give way to horizontal bands with striping that stand out against the very dark (greenish-black) feathers of the rest of the neck. Common Loon will have a more dramatically spotted back than Pacific Loon in breeding plumage, while Red-throated Loon does not develop spots at all in breeding plumage. Most Common Loons seen in Sonoma County will look like the bird in the upper photo on this page. Even the few birds that stay over the summer months at Bodega Bay each year often retain their "winter" or non-breeding plumage (the photo was taken at the end of April). Note that birds in different plumages may be present at the same time. The bird in the second photo below is rather unusual. It's in the middle of its molt into breeding plumage. The horizontal bands have developed on the neck, but some of the winter feathers are intact, creating a blotchy look that is atypical. However, the photo shows the heavy bill and flat-top look of the head.

At a distance, Common Loon and other loons may sometimes be confused with Double-crested Cormorant, which is another mostly dark bird that rides low in the water like a loon and often swims with its head and bill slightly raised (suggesting Red-throated Loon). Get a good look at the face and bill, however, and there should be no confusion. Also, Double-crested Cormorant tends to stay inland, near freshwater lakes. The loons are mostly (although by no means exclusively) marine birds when we see them in numbers, usually in the winter. Double-crested Cormorant and loons will overlap at estuaries, however (for example, at the mouth of the Russian River).