A practical guide to bird watching in Sonoma County, California

(Unless otherwise indicated, all phone numbers are in the 707 area code)


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.


Further reading:

Bolander and Parmeter, Birds of Sonoma County California, rev. ed., 2000, p. 13

Brinkley, National Wildlife Federation Field Guide to Birds of North America, 2007, p. 67

Dunn and Alderfer, eds., National Geographic Field Guide to the Birds of North America, 5th ed., 2006, p. 70

Dunn and Alderfer, eds., National Geographic Field Guide to the Birds of North America, 6th ed., 2011, p. 68

Dunne, Pete Dunne’s Essential Field Guide Companion, 2006, pp. 88-89

Ehrlich, Dobkin, and Wheye, The Birder's Handbook, paperback edition, 1988, p. 4

Fix and Bezener, Birds of Northern California, 2000, p. 39

Floyd, Smithsonian Field Guide to the Birds of North America, 2008, p. 74

Kaufman, Field Guide to Birds of North America, 2000, p. 66

Kaufman, Advanced Birding, 1990, pp. 20-29 (Notes on loon ID generally)

Kaufman, Field Guide to Advanced Birding, 2011, pp. 168-181 (Notes on loon ID generally)

Lukas, Bay Area Birds: From Sonoma County to Monterey Bay, 2012, pp. XX

Parmeter and Wight, Birds of Sonoma County California, Update (2000-2010), 2012, p. 12

Peterson, Birds of Eastern and Central North America, 5th ed., 2002, pp. 26, 44

Peterson, Field Guide to Birds of Western North America, 4th ed., 2010, p. 64

Peterson, Western Birds, 3rd ed., 1990,  p. 24

Sibley, Field Guide to Birds of Western North America,1st ed., 2003, p. 27

Stokes, Stokes Field Guide to the Birds of North America, 1st ed., 2010, p. 75

Vuilleumier, American Museum of Natural History, Birds of North America: Western Region, 2011, p. 72

Voice: Cornell Lab of Ornithology: All About Birds--Pacific Loon



© Colin Talcroft, 2009, 2010, 2011, 2012, 2013

Unless noted, all photos by the author. If you would like to use one of my images, please ask for permission for non-commercial use with proper credit or commercial use with proper compensation.


Young Pacific Loon, non-breeding plumage, Porto Bodega, Bodega Bay, December 13, 2011

For comparison: Common Loon in "winter " (non-breeding) plumage

North-end Bodega Harbor, June 24, 2011

Note: Squarish head; heavier, chiseled bill; "notched" neck pattern of light and dark

For comparison: Young Red-throated Loon in "winter " (non-breeding) plumage

Bodega Bay, December 12, 2011

Note: Light, straight bill; speckled rather than scalloped back pattern in this young bird

Pacific Loon

Common Loon

Red-throated Loon

Pacific Loon

Gavia pacifica

1990-2013 Sonoma County data. Graph provided by eBird (www.ebird.org), generated July 29, 2013

EBird reported occurrence in Sonoma County