||I photographed this bird on Isla San Francisco in the Gulf of California, and at the time I thought it was a California Gnatcatcher. Its call had a whiny mewing tone, which excludes Black-tailed Gnatcatcher -- and at the time I thought this was the only other possible species. But on checking my books, I see that Blue-gray Gnatcatcher is also possible in the Gulf, and I can't exclude that species based on what this photograph shows, or what I recall having heard. (Blue-gray has a single-note call, California a rising and falling tone -- both with a whiny or mewing tone.) The strong white eye-ring tilts toward Blue-gray. I don't have any notes on the appearance of the undertail, or a recollection of the voice that would separate California from Blue-Gray. I too readily assumed it was a California, mostly because an experienced birder on our tour had confidently identified another gnatcatcher on a nearby island as that species, presumably because the calls of the two species are quite distinct to anyone who has experience with both, as I do not.