In the 1830s, Massachusetts ornithologists recognized the Black Guillemot (not to be confused with the Foolish Guillemot, later known as the Common Murre) as an irregular visitor on the winter coast (Peabody 1839). By the 1860s, its status changed to “not uncommon,” and a definite southern expansion was occurring (Howe & Allen 1901). A line limiting this expansion was ultimately drawn, however, since the bird was rarely sighted south of Cape Cod. Generally, the Black Guillemot restricted itself to visiting the state during the colder months, and breeding on the coast from Maine northward. In Atlas 1, Black Guillemots were still known principally as winter birds, especially in areas along the North Shore where they were most common. Even so, the rapid expansion of the species’ wintering range, which once extended no farther south than Cape Ann, attracted the attention of birders throughout Massachusetts. Once Black Guillemots began breeding off New Hampshire on the Isles of Shoals, the short leap south to Massachusetts seemed inevitable. Despite a handful of historic summer records, no breeding evidence for this species was found during the time of Atlas 1 or Atlas 2.