Pacific Loon

Pacific Loon, like all loons that visit Sonoma County, is most common during the winter months, but also present (sometimes in large numbers) during spring and fall migration. Some birds may arrive as early as late August, but Pacific Loons begin to show up in force usually in late September to early October, staying through mid-April, with some birds lingering into early June. A few birds stay over the summer, but Pacific Loon is probably least common here in June and early July. Often seen singly or in small groups, but large flocks are sometimes visible off our coasts during migration. I've seen as many as 90 birds at once, near Jenner.

Distinctive in breeding plumage, but less so in the winter, or non-breeding, plumage we commonly encounter in Sonoma County. Identifying loons in winter plumage can be a challenge. We commonly see three species here: Common Loon (Gavia immer), Pacific Loon, and Red-throated Loon (Gavia stellata). Given a good look, there are enough differences to tell the various species apart, but too often we see loons in flight, at long distances, or bobbing on waves, all of which can make it hard to get an adequate set of clues to work with. In winter plumage, the coloration of the neck is perhaps the most reliable tool, but note that loons take three or four years to attain full adult plumage, which may complicate identification.

An adult Pacific Loon in non-breeding plumage is white at the chin, throat, and front of the neck, with silvery grey upper parts. Note the clear line between the pale front of the neck and the dark at the back of the neck. Common Loon in winter plumage has a notched look here (photo below). In Common Loon, the white cuts into the dark areas, creating a zig-zagged line where the separation is clean in Pacific Loon. Pacific Loon has a proportionately smaller, less chiseled-looking bill than Common Loon (again, compare photo below). It's worth looking carefully at the shape of the heads of these two birds. Common Loon has a squarish head, often appearing flat on top, sloping in front and in back of the flat area. Pacific Loon usually gives the impression of having a more smoothly rounded head. Although wet birds and birds with mussed feathers can be deceptive, given an opportunity to observe for a reasonable amount of time, general head shape should be apparent. Both birds are a fairly plain grey above in winter plumage. Younger birds of both species show pale edgings on the feathers of the back that create a scalloped look, as in the young bird in the photo above, but the pattern is finer and more delicate looking in Pacific Loon. Young Red-throated Loons have a speckled look (photo below). Pacific Loon usually shows a dark "chin strap," lacking in any other loon species, but this chin-strap may be nearly absent in some young birds (as in the bird in the photo above).

Compared with Pacific Loon and Common Loon, Red-throated Loon is a smaller bird with a proportionately small head, fine bill, and longish neck. The division between light and dark on the neck in winter plumage is diffuse, showing neither the notched or zig-zag look of Common Loon nor the neatly front-to-back vertically divided look of Pacific Loon. Red-throated Loon typically holds its bill tilted slightly upward, whereas Common and Pacific Loon tend to hold their bills more horizontally. Note that all loons swim low in the water and may at a distance resemble a cormorant. Mistaking cormorants for loons is a common error among beginning birders and one that even the most experienced may occasionally make--if for only a moment.

In breeding plumage, which we occasionally see on late-season dawdlers and birds that stay over the summer, the three common loon species we see in Sonoma County should be easy to separate by their distinctive plumages--Pacific Loon with its silvery-grey nape, dark foreneck, and vertical striping on the side of the neck; Common Loon with its strikingly dark-greenish black head and horizontal zones of black and white striping on the throat; and Red-throated Loon with the red patch at the foreneck that gives the bird its common name.

Trivia: Loons are unusual among birds in that they molt their flight feathers all at once, which renders them temporarily flightless for a few weeks.