282 BULLETIN 17 0, UNITED STATES NATIONAL MUSEUM 



the time of hatching. The other is the unaccountable fluctuation 

 in the weights of the youngsters, as illustrated by the graph." 



Plumages. — The sequence of plumages to maturity is the same as 

 given for the eastern screech owl. As in practically all the western 

 races, adults are to some extent dichromatic, though the color phases 

 are not so pronounced as in the eastern races. The gray phase of 

 quercinus is lighter gray, and the brown phase is duller brown than 

 in the more northern races. 



OTUS ASIO GILMANI Swarth 

 SAGUARO SCREECH OWL 



HABITS 



Ridgway (1914) does not recognize the validity of this race, and 

 says, in a footnote under cineraceus: "With a considerable series of 

 specimens before me, including those upon which 0. a. gilmani Swarth 

 was based, I am quite unable to appreciate reasons for the recognition 

 of that supposed subspecies; indeed, few of the recognized subspecies 

 of the group present as great uniformity of coloration as does this 

 series as a whole." He also thought that the difference in size is 

 insignificant, and he could not accept the theory of two subspecies 

 occupying such closely contiguous territory. 



Mr. Swarth (1916), however, seems to have explained the situation 

 very satisfactorily, and to have established the validity of his race, 

 after an extensive study of a series of thirty screech owls from various 

 parts of southern Arizona. He concludes that — 



there are two distinct types represented, cineraceus from the higher mountains, 

 gilmani from the valleys of southwestern Arizona. Breeding birds from either 

 region are true to type in their appearance. Extremes of the gilmani character- 

 istics appear at points farthest from the known range of cineraceus (as at Phoenix 

 and on the Colorado River). At one point at the margin of the habitat of gilmani 

 (as I conceive it) there occur in winter examples of cineraceus. 



There are certain facts in the distribution of screech owls in Arizona which 

 deserve to be emphasized. My conception of Otus a. gilmani is of a bird of the 

 hot Lower Sonoran valleys, and of Otus a. cineraceus, as one pertaining 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 sub- 

 species to be capable of definition on other terms than those of life zones. In 

 southeastern Arizona, the region of the scattered mountain ranges where cinera- 

 ceus occurs, the intervening valleys and plains, of vast extent, are for the most 

 part grass covered, or else with but a sparse growth of mesquite or larrea, in 

 neither case supplying habitable surroundings for the screech owl. Farther west, 

 from the Santa Rita and Santa Catalina mountains westward, the endless stretches 

 of Lower Sonoran plains where gilmani 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 Arizona the Lower Sonoran zone offers congenial 

 surroundings to screech owls, in southeastern Arizona for the most part it does 

 not. In southwestern Arizona, Lower Sonoran is the only life zone represented, 

 in southeastern Arizona the higher zones occur, with associational conditions 

 acceptable to these owls. 



