Sandwich Tern candidate – San Diego River

[All photographs copyright, Gary Nunn 2013] – I’ve been observing the growing “tern show” spectacle at the San Diego River flood control channel for a few days. Viewed from Robb Field in Ocean Beach the numbers peak late morning and late afternoon. Numerically dominated by Elegant Tern, there are also good numbers of the stocky looking Royal Tern, and a handful of demure Forster’s Tern nervously putting up with the racket. Spooked by raptors – Osprey, Merlin, and Peregrine all made a pass – the noise from the erupting 400-500 Elegant Terns is pretty intense right in front of you viewed from the bike path. But my main reason for visiting twice a day was to look for terns with dark bills. After photographing several Elegant Terns with “parti-colored” black marked bills I finally hit upon a serious candidate for an American race of Sandwich Tern Thalasseus sandvicensis acuflavida. This species of tern is headed for radical taxonomic changes and we will all, most likely, know it as Cabot’s Tern by year end.

Sandwich “type” Tern – San Diego River at Robb Field, 31 March 2013

Sandwich “type” Tern – San Diego River at Robb Field, 31 March 2013

Sandwich “type” Tern – San Diego River at Robb Field, 31 March 2013

Recent research has shown that the North American acuflavida tern is virtually indistinguishable genetically from the Caribbean-South American eurygnatha tern known as Cayenne Tern. This makes a lot of sense considering the mixed breeding colonies of these two forms known in the Southern Caribbean. What we know as Sandwich Tern in North America is actually not most closely related to the nominate sandvicensis tern from Europe. Nineteenth century taxonomy was actually pretty good in many respects and it looks as if, based on precedence, we will again be using the delightful patronym Cabot’s Tern, which will comprise the New World nominate acuflavida (black-billed) and the southern eurygnatha (yellow-billed) forms. Interbreeding of these two forms at breeding colonies, and the myriad black and yellow bill color patterns produced, will be the subject of another post!

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