Caspian Tern

Hydroprogne caspia

The largest tern, Caspian Tern is a fairly common summer visitor to Sonoma County, probably best seen at Bodega Bay or around Jenner, at the mouth of the Russian River, where you can watch them hovering over the water and then diving for fish. Birds may arrive as early as late March and usually stay until around mid-October. Although adults can sometimes be seen feeding immature birds mid-summer, Sonoma County Breeding Bird Atlas has no confirmed breeding records for the county (according to The Birder's Handbook, Caspian Terns feed immature birds for as long as 5-7 months after fledging). In 2006, Caspian Tern was moved to the genus Hydroprogne. Older sources will list this bird as Sterna caspia.

The size of a fairly large gull. Recognized by its size (about 21 inches or 53cm bill to tail); heavy, deep red bill with blackish tip; black cap; clear, pale grey upper wings; black at the wingtips visible from below; black feet; and a comparatively shallow fork in the tail. When standing, the head looks large and squarish. Seen in flight, the heavy red bill and shallow tail fork are perhaps easiest to see. In winter (and juvenile) plumage, the black cap becomes streaky, but it always extends over the entire forehead, unlike any of the other terns we see in Sonoma County--mostly Elegant Tern (Thalasseus elegans), Forster's Tern (Sterna forsteri), occasionally Common Tern (Sterna hirundo) and rarely Arctic Tern (Sterna paradisaea), this last usually well offshore and during migration only. Setting aside Arctic Tern, Elegant Tern is a smaller bird (about 17 inches or 43cm), with a much more slender bill, a white forehead in winter plumage, and a distinctive shaggy crested look (always reminding me of a black-haired man bald except at the back of the head that has let his remaining hair grow long). Forster's Tern, also a markedly smaller bird than Caspian Tern (at about 15 inches or 38cm) has a deeply forked tail; a black cap in breeding plumage that extends further down the nape; a lighter, more slender bill than Caspian Tern; and red feet rather than black feet. In winter plumage, Forster's Tern is easy to pick out because it loses its black cap almost entirely while retaining black around the eye, making it look like it has a "black eye." Note that Forster's Tern is the only tern normally present in Sonoma County during the winter months.

Finally, a note of caution: As with the gulls, the terns can be 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 and hunkered down on the ground. No one field mark is ever reliable. 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.)

Further reading: National Geographic Field Guide to the Birds of North America, 5th ed., 2006, pg. 218; Peterson, Western Birds, 3rd ed., 1990, pg. 104; Peterson, Field Guide to Birds of Western North America, 4th ed., 2010, pg. 174, 190; Sibley, Field Guide to Birds of Western North America,1st ed., 2003, pg. 202; Birds of Sonoma County California, rev. ed., 2000, pg. 64; The Birder's Handbook, paperback edition, 1988, pg. 192; Peterson, Birds of Eastern and Central North America, 5th ed., 2002, pg. 186; Kaufman, Field Guide to Advanced Birding, (notes on identifying terns generally; pages 272-284).

Voice: Cornell Lab of Ornithology: All About Birds--Caspian Tern

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Caspian Tern: Note heavy dark red bill; black at the tips of the undersides of the wings

Caspian Tern: Note heavy dark red bill; clear, pale grey upper sides of the wings, shallow fork in the tail

Size comparison: Elegant Tern in the foreground, Caspian Tern behind. In addition to its greater size, note Caspian Tern's large, squarish head; heavy, red bill.

Bodega Bay, July 6, 2011

For comparison: Forster's Tern (winter plumage)--Note shorter, lighter bill (black in in non-breeding, winter plumage); mostly white head with black around the eye; red feet

Caspian Terns standing

Bodega Bay, July 6, 2011