Those are Forsters Terns. We have them here in Huntington Beach along the Coast and nesting sites in Bolsa Chica Wetlands. Here is one of my shots of them amongst Willets and Marbled Godwits.
Forster's don't seem to have the black tip on the bill or black-edged wings. Am I correct?
Ken, the suggestions you have already got would be what my books would also ID them as, which one I am not sure. The common tern would also be added to the list. The colors on the bill is the main thing I am going by along with where they are normally seen. The photo is great.
Greg
Thanks, Greg. I am going with Least Tern at this point.