here is some speculation as to the Northern Gannet's provenance as discussed on the Pacific Seabird Listserv.

Approximately two years ago, on April 25, 2012, Sophie Webb reported a Northern Gannet from Southeast Farallon Island, found by Peter Warzybok earlier in the morning.

Seabird Biologist Bob Day reported: "Maybe this is the one that our folks saw in the offshore northeastern Chukchi Sea in 2010. Unfortunately, we never were able to get a photo. Other scientists saw it a few days later near Barrow. The Northwest Passage was open that summer, and we suspect that the Gannet came through then, perhaps following some ships? There also were records of Great Black-backed Gull on the North Slope that same summer." R. H. Day.

And for the long view, Storrs L. Olson, Curator Emeritus of Birds for the Smithsonian Institution wrote: "Well, there were gannets there in the Pleistocene, so I guess it was only a matter of time. That one will report back and they will be breeding in California in a couple of decades."