|Juvenile Elegant Tern. Oceanside, California. September 28, 2014. Greg Gillson.|
Black hind crown feathers encircle eye. Thin, yellower bill.
Caspian Terns are regular throughout the year, especially common in summer. Elegant and Royal terns were formerly more restricted in timing. Elegant Terns were most common from July through October and Royal Terns were most common from November through February (Birds of Southern California: Status and Distribution. 1981. Kimball Garrett and Jon Dunn).
But in more recent years both Elegant and Royal terns have expanded their presence. eBird data for San Diego County (below) shows Elegant Terns occur from March into November and Royal Terns are expected throughout the year, though slightly less common in spring.
Caspian Terns are larger than Royal and Elegant terns. The length (bill tip to tail tip) shows some difference (Caspian 21 in., Royal 20 in., Elegant 17 in.), but wing span gives a better idea of the size difference (Caspian 50 in., Royal 41 in., Elegant 34 in.). The smaller Elegant Tern is more delicate, quite obvious in flight.
In flight, the undersides of the primaries are mostly black in Caspian Terns. In Royal Terns the outer primaries are black underneath, but the base is pale. The undersides of the primaries of Elegant Terns are mostly pale with only black tips.
The bill of Caspian Tern is red-orange and heavy. The bill of Elegant Tern is yellow-orange, rather slender and slightly down turned. The bill of Royal Tern is orange, in between Caspian and Elegant in thickness.
|Adult non-breeding Royal Tern. Oceanside, California. September 28, 2014. Greg Gillson.|
Eye separated from black hind crown. Stout orange bill.
Non-breeding Royal Terns have the most reduced black crown, with white around the eye and a short black crest on the hind crown. Elegant Terns have black feathers around the eyes and a longer black crest on the hind crown. Caspian Terns in non-breeding plumage never show a fully white forehead as do the other two terns. Instead the fully black crown is streaked with white.
|Adult Caspian Tern. August 7, 2009. Newport, Oregon. Greg Gillson.|
Note Heavy reddish bill.