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July, 1916 SAHUARO SCREECH OWL AS A RECOGNIZABLE RACE 165 to Upper Sonoran, oak-covered foothills and canyons. But I believe that a sufficient representation of specimens would show the respective ranges of the two subspecies to be capable of definition in other terms than those of life zones. In southeastern Arizona, the region of the scattered mountain ranges where cineraceus occurs, the intervening valleys and plains, of vast extent, are for the most part grass covered, or else with but a sparse growth of mes- quite or larrea, in neither case supplying habitable surroundings for the screech owl. Farther west, from the Santa Rita and Santa Catalina mountains west- ward, the endless stretches of Lower Sonoran plains where giImani is found are grown up nearly everywhere with the giant cactus, which supplies so many hole-dwelling birds with homes. In other words, in southwestern Ari- zona the Lower Sonoran zone offers congenial surroundings to screech owls, in southeastern Arizona for the most part it does not. In southwestern Ari- zona, Lower Sonoran is the only life zone represented, in southeastern Ari- zona the higher zones occur, with associational conditions acceptable to these owls. Certain parts of the foothill region of the Santa Rita and Santa Cata- lina mountains are where the widely different zonal and associational condi- tions of the eastern and western extremes find a meeting place. It is in this region that conditions occur that predicate the possibility of finding both of the subspecies of Otus asio here treated (as we ace has been the case), or of find- ing specimens intermediate in their characters between the two extremes. There are specimens from Fort Lowell at hand that might be regarded in this light. It may be said here that the Lower Sonoran areas of southeastern and southwestern Arizona, respectively, are widely different in their general aspects, and contain strongly contrasted assemblages of animal and plant life. There still remains to be accomplished, as a highly desirable piece of zoological work, a critical comparative study of the animal life of certain of these closely adjacent but faunally unlike valleys. As to the characters of color and markings distinguishing cineraceus and giImani, these are such as can not well be demonstrated other than by asser- tion. I can merely re-affirm that the screech owls of the Otus asio group from southern Arizona are of distinguishable types from two definable regions, exhib- iting color differences readily apparent to the eye. In measurements it will be seen from the accompanying table that, although the differences are not great, the maximum of size is in cineraceus, the minimum in giImani. MI?ASURE?MI?NTS IN MILLIME?rI?P? OF Olus a$1o ineraceu$ AND O. a. ?ilmanl Wing Tall Bill (from nastril to tip) Otus asio cineraceus : 4 nmles from Htmchuca ?nd Chirica- hu? Mts., Arizona Otus asio gilmani: 4 males from Fort Lowell and Blackwater, Arizona Otus asio cineraceus: 4 females from Huachuca and Chirica- hua Mts., Arizona Otus asio gilmani: 4 females from Tucson, Phoenix, Col o' rado R., and Blackwater, Ari- zona Berkeley, California, June 20, 1916. 164.7 (149.0-160.0) 150.0 (147.0-155.0) 161.7 (157.0-168.0) 153.2 (150.0-156.0) 79.2 (77.5-82.0) 74.2 (73.0-76.0) 64.1 (82.5-86.0) 77.1 (74.0-80.5) 10.7 (10.5-11.0) 10.5 (10.0-11.0) 10.8 (10.2-11.2) 10.8 (10.6-11.0)