from: :S.F. Baird and others, 1884, The Water Birds of North America, about the Clark's Grebe:
"... This form, which bears a very strong resemblance to AEchmophorus occidentalis [Western Grebe], was regarded by Mr. Lawrence [1858] as being a distinct species, but is now considered as only a variety. While it thus strongly resembles the occidentalis in size and in some of its markings, it constantly differs. The two seem to have nearly the same habitat; and as it is not usual for two races of the same species to swell in exactly the same area, it seems more probably either that the differences are specific, or that they possess some sexual or other significance, unless the present form should be found to have a more southern range. The first known specimen of this form was taken by Mr. J.H. Clark in Chihuahua, Mexico, and other specimens were procured from the sea-coast of California at Santa Barbara and on San Pueblo Bay. ..." -- [S.F. Baird, T.M. Brewer, and R. Ridgway, 1884, The Water Birds of North America: Little, Brown and Company, Boston, v.II, p.424]