The most obvious difference between the local wintering Black-throated Divers are that they are all in full winter plumage, whereas this Pacific Diver still shows some summer plumage. This feature was one of the original pointers to its' identity. In addition, Black-throated Diver is rare at Carnsew Pool.
There are two other records for the UK, both juveniles. The first UK record was a juv at Farnham GP, 12th Jan to 4th Feb 2007. The second record was at Llys-y-Fran reservoir from the 2nd Feb to 20th Mar 2007. From memory (correct me if wrong), this bird also reappeared at the same site, so there is obviously some site fidelity shown by Pacific Divers. Another bird was also seen last week in Gloucestershire though at the time of writing, I don't have any more info on this individual.
Pacific Diver breeds NE Siberia , and north North America from Alaska east to Hudson Bay. Winters in the Pacific Ocean, in Asia south to Japan and East China and in North America south to California and Mexico.
EXIF Detail: In poor light and rain. Aperture wide open at F/5.6. Shutter 1/250s. ISO 500. Exposure 0.0EV. Focal length 840mm. Tripod mounted.