"White" Pigeon Guillemots in August might be one-year-old birds that never
entered breeding plumage.

Juvenile Pigeon Guillemots--at least all I've seen--are dark, mostly dark
brown to blackish above and white below with variably extensive white wing
markings (some don't have a trace of white on the wing). Rarely they are
almost entirely dark. They have been mistaken for murres or murrelets by
many people. They have never been adequately illustrated and are often (or
typically) darker than the "juvenile" shown in the NGS field guide.

Dennis Paulson, Director phone 206-756-3798
Slater Museum of Natural History fax 206-756-3352
University of Puget Sound e-mail dpaulson at ups.edu
Tacoma, WA 98416