A practical guide to bird watching in Sonoma County, California

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


Forster's Tern is the only tern normally present in Sonoma County in the winter. Probably best seen at Bodega Bay or around Jenner, at the mouth of the Russian River. Most common in the autumn months, less so in others, and not normally present in June. The bird in the photo above is in non-breeding (winter) plumage.    

The size of a small gull. Recognized in breeding plumage by its small size (about 15 inches, or 38cm, bill to tail); slender, mostly orange bill with blackish tip; black cap; pale grey back and very pale wings that tend to be paler toward the tips when seen from above (although usually with some darkening at the very edges of the wingtips--that is, the tips of the outer primaries are darker); red feet; deep fork in the tail (although the fork in the tails of many terns is created by longer outer tail feathers, and molting can cause a forked tail to appear different at different times).

In winter (and juvenile) plumage, the black cap is absent (although it may remain to some extent at the back of the head), and a wash of black continues to cover the area around the eye, giving the bird the look of having a "black eye" (photo above). Note that the shape and extent of the black wash over the eye is somewhat variable. Note also that in non-breeding (winter) plumage, the bill darkens and may be entirely black, as in the bird pictured above, although a little dusky red is often retained at the base of the bill.  

Forster's Tern is the only tern usually present in the county in the winter months. Overlaps with Elegant Tern (Thalasseus elegans) and Caspian Tern (Hydropogne caspia) mostly between July and October, and less commonly Common Tern (Sterna hirundo) which is a very occasional visitor here between mid-August and mid-November. Arctic Tern (Sterna paradisaea) may be present mid-July to Mid-October, but this last is very uncommon in Sonoma County and usually seen (if at all) well offshore. In breeding (summer) plumage, Forster's Tern is unlikely to be confused with Caspian Tern, which is set apart by its very large size, deep red bill, black wingtips when seen from underneath, and black legs. Elegant Tern, also a noticeably bigger bird, has a distinctive shaggy crest, and a very long, thin, slightly down-curved yellow-orange bill. Forster's Tern is most similar in appearance to Common Tern, but that bird (despite the name) is not common in Sonoma County. Perhaps the most obvious features useful in distinguishing Common Tern and Forster's Tern in breeding plumage are the thicker, more orange-red bill of Forster's Tern (Common has a thinner bill that tends to be redder), and the darker wingtips of Common Tern. It may also be useful to remember that Forster's Tern always has red legs. Common Tern has red legs in breeding plumage, but these darken to near black in non-breeding plumage. However, to repeat, Common Tern is unusual here, unusual enough that local bird watchers get excited if a Common Tern shows up.

Finally, a note of caution: As with the gulls, the terns are variable and plumages change with age and season. While I believe the general points above to be accurate and useful, terns can be quite confusing, not least because they are often seen at a distance and on the wing, or at a distance hunkered down on the ground. If you're serious about learning terns, I recommend the detailed discussions in the Kaufman guides listed below. (That said, Caspian Tern and Elegant tern are usually not big identification problems among the terns in Sonoma County. The biggest mistake is probably assuming that all summer (breeding plumage) terns here that look like a Forster's Tern actually are Forster's Terns without really taking a good look to see if you might have a Common Tern, or, less probably, an Arctic Tern. While chances are good that it is a Forster's Tern, it's worth looking to be sure.)

English synonyms: None

Forster’s Tern in other languages--German: Forster-Seeschwalbe, Sumpf-Seeschwalbe; Spanish: Carrán de Forster, Charrán Cejinegro, Charrán de Forster, Gaviota de Forster, Gaviota golondrina de Forster, Gaviotín de Alas Blancas, Golondrina del Mar, Golondrina-marina de Forster; French: Sterne de Forster; Italian: Sterna di Forster; Dutch: Forsters Stern, Forster-stern; Russian: Крачка Форстера; Japanese: メリケンアジサシ  (merikenajisashi); Chinese: 弗氏燕鸥

(Language information from Avibase, Birds of Europe (Mullarney et al, Princeton Field Guide Series), and Birds of Asia (Mark Brazil, Princeton Field Guide Series).

Further reading:

Bolander and Parmeter, Birds of Sonoma County California, rev. ed., 2000, p. 65

Brinkley, National Wildlife Federation Field Guide to Birds of North America, 2007, p. 140

Dunn and Alderfer, eds., National Geographic Field Guide to the Birds of North America, 5th ed., 2006, p. 220

Dunn and Alderfer, eds., National Geographic Field Guide to the Birds of North America, 6th ed., 2011, p. 240

Dunne, Pete Dunne’s Essential Field Guide Companion, 2006, pp. 285-286

Ehrlich, Dobkin, and Wheye, The Birder's Handbook, paperback edition, 1988, p. 184

Fix and Bezener, Birds of Northern California, 2000, p. 187

Floyd, Smithsonian Field Guide to the Birds of North America, 2008, p. 198

Kaufman, Field Guide to Birds of North America, 2000, p. 88

Kaufman, Advanced Birding, 1990, pages 134-149 (Chapter 18 "The Medium-sized Terns")

Kaufman, Field Guide to Advanced Birding, 2011, pp. 272-284 (notes on identifying terns generally) and pages 284-299 (Chapter 19 "The Medium-sized Terns" 134-149)

Lukas, Bay Area Birds: From Sonoma County to Monterey Bay, 2012, pp. 134-135, 137, 292

Parmeter and Wight, Birds of Sonoma County California, Update (2000-2010), 2012, p. 37

Peterson, Birds of Eastern and Central North America, 5th ed., 2002, p. 188

Peterson, Field Guide to Birds of Western North America, 4th ed., 2010, p. 188

Peterson, Western Birds, 3rd ed., 1990,  p. 106

Sibley, Field Guide to Birds of Western North America,1st ed., 2003, p. 204

Stokes, Stokes Field Guide to the Birds of North America, 1st ed., 2010, p. 353

Vuilleumier, American Museum of Natural History, Birds of North America: Western Region, 2011, p. 178

Voice: Cornell Lab of Ornithology: All About Birds--Forster's Tern



© Colin Talcroft, 2009, 2010, 2011, 2012, 2013, 2014

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.


For comparison: Elegant Tern in foreground. Note long, yellow-orange bill; shaggy crest; black legs. Caspian Tern in background. Note large size, squarish head, heavy red bill

For comparison: Caspian Tern in flight--Note heavy, dark red bill; pale upper wing; shallow fork in tail

Forster's Tern

Sterna forsteri

Forster’s Tern, Alameda (Alameda County), November 22, 2010

1990-2013 Sonoma County data. Graph provided by eBird (www.ebird.org), generated July 1, 2013

EBird reported occurrence in Sonoma County