191^] Griiniill: Mammals and Birds of the Colorado Valhij 129 



Bubo virginianus pallescens Stone 



Western Horned Owl 



The hooting of liorned owls was heard almost nightly at every one 

 of our camps, from Needles to Pilot Knob. The birds themselves were 

 occasionally seen flying overhead at dusk, and twice, on the California 

 side at Riverside IMountain and opposite Cibola, were flushed in the 

 daytime from dense ironwood trees in desert washes back from the 

 river. Three specimens were shot (nos. 12702-12704). These are 

 markedly pale, as compared with Bubo virginianus pacificus of the 

 coastal slope of southern California, and in their characters closely 

 approximate specimens from central Arizona which in turn have been 

 refei-red to B. v. pallescens (see Oberholser, 1904, p. 182). 



Micropallas whitneyi (Cooper) 

 Elf Owl 



The elf owl was detected only in the belt of saguaros which extends 

 across the Colorado Valley within six miles above the Laguna Dam. 

 The numerous excavations in the trunks of these great cactuses evi- 

 dently furnish desirable diurnal retreats for owls of size small enough 

 to render them usable. By chopping into many of the perforated 

 saguaros we succeeded in capturing two of this species, nos. 12700 and 

 12701. The latter was taken on the Arizona side, April 22. from a 

 hole twelve feet above the ground. The cactus in which it was located 

 wa.s a single column thirty-one feet high and twenty-six inches in 

 diameter. In the same tnink, four and one-half feet higher up, was 

 an occupied nest of the gilded flicker. The other bird was taken 

 April 23 on the California side four miles above Potholes. The cavity 

 occupied in this instance was twelve feet above the ground in a three- 

 branched saguaro eighteen feet tall and twenty-six inches in diameter. 



In the same trunk one foot lower, but opening on the opposite side, 

 was a cavity occupied by a sparrow hawk and its five eggs. Both owls 

 were females, and each showed signs of immediate breeding. In one 

 case dissection disclosed five large ova of graded size, the largest being 

 an apparently full-sized yolk. 



The locality where our California specimen was secured is some 

 two miles west of the river and not far from the old Senator ]\rine. 

 It is in a valley leading down from the hills and locally known as 



