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 206 Vol. XXIV DISTRIBUTION OF MOLOTHRUS ATER IN CALIFORNIA WITH THE DESCRIPTION .OF A NEW RACE By DONALD R. DICKEY and A. J. VAN ROSSEM URING the late spring and summer of 1920, the writers took a series of cowbirds at Buena Vista Lake, Kern County, California. Pressure of other work prevented careful diagnosis at the time, and since birds of t.hat region had previously been referred to Molothrus ater obscurus, that name was tentatively applied to these specimens. On further examination this series showed such a definite departure in characters from those exhibited by a large collection of obsctrus from the Colorado Desert and adjacent regions, as to make a thorough analysis of the status of cowbirds in California seem advisa- ble, With this end in view, we have assembled or examined all of the material available in the Museum of Vertebrate Zoology and the Museum of History, Science and Art, together with many individual specimens gathered from pri- vate sources. Our thanks are due not only to those in charge of the ornitholog- ical collections of the institutions mentioned above, but also to the several pri- vate collectors who have so courteously placed their material at our disposal. The resultant data has served-to emphasize the fact that much remains to be done in the way of systematic collecting even in a State that has been as thoroughly canvassed as California. In the present instance there is adequate material from southern California, north to Mono Lake on the east, to Merced County in the San Joaquin Valley, and to Oxnard, Ventura County, on the Pacific Slope. North of these points we have been able to trace only a single specimen from the Modoe region, a stray migrant from the Farallon Islands, and t. wo non-breeding birds from Santa Barbara County. Cowbirds are known to occur in fair numbers at various intermediate points, but specific records seem unexpectedly scarce and specimens lacking. A general impression seems to have sprung up that cowbirds have only recently invaded California.- It is unquestionably true that their numbers have increased greatly during the past few years, but in our belief this is due simply to natural increment rather than influx, and is adequately explained by the increasingly favorable conditions that have.inevitably resulted from the present extensive development of dairying, truck-gardening, and irrigation projects in general. So far as we can determine there is no reason to suppose that Cow- birds, in small numbers, have not always been residents of the area. J. Grin- nell() and Edward Wall(2)have already made some very pertinent remarks on this subject: Molothrus ater obscurus (Gmelin) Dwarf Cowbird Range in California: Southern California, from the Arizona line west to San Diego; north over the Colorado and Mojave deserts to Death Valley, the Panamint Mountains, and Independence, Inyo County; north through the San Diegan district to the vicinity of Ventura and, in winter at least, to Goleta, Santa Barbara County. Specimens examined (approximately 150) from the (D Univ. Calif. Publ. Zool., 5, 1909, pp. 275-281. (2) Condor, 21, 1919, p. 209.