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 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 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 see 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 
gilmani, 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 gilmani. 
MEASUREMENTS IN MIIJJMETERS OF Olus asio cineraceus AND O. a. gilmani 
Wing Tail Bill 
(from nostril to tip) 
Otus asio cineraceus : 4 males 
from Huachuca and Chirica- 
hua Mts., Arizona 
Otus asio gilmani : 4 males from 
154.7 (149.0-160.0) 
79.2 (77.5-82.0) 
10.7 (10.5-11.0) 
Fort Lowell and Blackwater, 
Arizona 
Otus asio cineraceus: 4 females 
150.0 (147.0-155.0) 
74.2 (73.0-76.0) 
10.5 (10.0-11.0) 
from Huachuca and Chirica- 
hua Mts., Arizona 
Otus asio gilmani : 4 females 
161.7 (157.0-168.0) 
84.1 (82.5-86.0) 
10.8 (10.2-11.2) 
from Tucson, Phoenix, Colo- 
rado R., and Blackwater, Ari- 
zona 
153.2 (150.0-156.0) 
77.1 (74.0-80.5) 
10.8 (10.5-11.0) 
Berkeley, California, June 20, 1916. 
