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 z28 THE CONDOR Vol. III Selasphorus rults is typically a bird of the Humid Northwest Coast Boreal (of Merriam). The extreme of brown coloration is reached in both sexes of this species; and it is a matter of long observation that the brightest browns are developed in birds of that region, whether resident, or present only dur- ing the breeding season as in the case of the Rufous Hummer. For it is also known that the breeding environ- ment of migratory species is much more potent in its effects than is their envi- ronment during the rest of the year. Now the Humid Northwest Coast Boreal extends southward along the Pacific Coast from the vicinity of Sitka, Alaska, to Humboldt Bay, California (fide Merriam). S. rufus breeds abund- antly in most of this faunal area, and thus if it breeds at all in California I should expect to find it in the Humboldt Bay region, but not south of that vicin- ity. Selasphorus alleni is known to breed abundantly in the San Francisco Bay region and north through Marin County and south through the Santa Cruz and Santa Lucia Mountains to the Santa Barbara Islands. Now the "San Francisco Bay Region" is principally Humid Upper Sonoran, and the narrow coast belt to the north up to Humboldt Bay and southward through the Santa Lucias is Humid Pacific Coast Transi- tion as well as Humid Upper Sonoran. S. alleni appears to be exclusively a breeding bird of this Humid Transition and Hunlid Upper Sonoran, and I do not know of its breeding outside of those faunal areas. The Allen Hum- mer is characterized by a less extensive brown coloration in both sexes than the Rufous. This is according to our theory, for the humidity and cloudy weather is less in the summer habitat of the former than in that of the latter. But the considerable amount of brown of X. aileni still shows it to be a normal inhabitant of a moderately humid area. And, in fact, do we ever find it breed- ing in any of the arid portion of the interior and Southern California? It seems to me probable, therefore, that the form alleni has evolved in this southern less humid coastal area at first as a geographical race or subspe- cies of X. rufus. Or, perhaps, since the. origin of the hummingbirds is undoubt- edly neotropical, the reverse was the case; that is, that rufus evolved from a lighter-colored ancestor more nearly like alleni. At any rate my point is that Xelasfihorus allertl and X. rufus should be as yet confined to separate zonal or faunal areas in the breeding season. I believe geographical isola- tion to be absolutely essential to the differentiation of two forms. X. alleni and S. rufus are very much alike; their distinguishing characters are slight and not altogether constant, and perhaps intergradation may still exist some- where in the Humboldt Bay region. I do not think it quite reasonable to ex- pect to find two such close forms breed- ing in the same locality or even any- where in the same fauna, such as in- cludes the San Francisco Bay region, where X. rufus has been reported nest- ing so often, but where I know that S. allertl is a very common breeder. Of course it is possible, even accept- ing the above doctrine, that after the complete differentiation of the two forms and disappearance of interme- diates, S. rufus may have invaded the breeding habit of X. allertl, and that the two species may thus now nest in the same area. And this is undoubtedly what has happened in the case of other species of hummingbirds breeding in the same locality, but which are much more remotely related. Yet it seems to me that the present case is not so far properly proven. It must be kept in mind that both S. rut'us and q. alleni occur broadcast during the migrations, and the males, immediately after mat- ing may wander many hundred miles in search of favorable feeding grounds, and thus occur at the same season and in the same locality with other breed- ing species of hummingbirds, mingling with them in combat or play. I there- fore repeat the query made in the May CONDOR. JOSEPH GRINNELL.