BLACK ROSY FINCH 367 



attempting to display before a female was almost blown off his feet 

 in the process. 



The territory of these birds is unusual in that it centers around the 

 female bird. It moves wherever she moves, even if it means leaving 

 nest and eggs unguarded. Whether the female is feeding, selecting 

 a nest site, or buUding a nest, her mate stays with her and continually 

 has to drive away the one to several males constantly trying to attract 

 her attention. This situation apparently results from the dearth of 

 females. All observations in both winter and summer indicate that 

 males outnumber females approximately six to one. The actual 

 causes of this unbalanced sex ratio, which can hardly be advantageous 

 to the birds, remain obscure. 



Another consequence is that the entire work of selecting a nest site 

 and building the nest falls to the female, the male beixig quite occupied 

 by others of his kind. One female examined potential nest sites on 

 a cliff for 8 days before finally deciding upon one and beginning nest 

 construction on the ninth day. The nest is usually completed in 3 

 days. Nest building has been observed as early as June 11 and as 

 as late as July 14. 



The nest is placed in a crevice or hole at some almost inaccessible 

 location on a vertical cliff. It is thus well protected from above and 

 on all sides but one, which remains as an entrance. In a single un- 

 usual case the female had built her nest among the rocks of a talus 

 slope where it was practically as well protected. The nest itself is a 

 cupped structure, completely supported from below except when the 

 sides happen to rest against the walls of the nest cavity. The base 

 is generally of mosses, which may be growing in the cavity, and the 

 upper portion is made primarily of gi'ass, with some feathers, hair, 

 and moss mixed in. The lining is of finer grass and hair. 



Eggs. — Of the eight sets of eggs that have been observed, including 

 three sets reported by F. W. Miller (1925), three nests contained five 

 eggs, four nests contained four eggs, and one contained three eggs. 

 The last of these was a replacement after the first set was destroyed, 

 which may account for the small number. The egg is pure white and 

 ovate pyriform in shape, giving the impression of being rather long 

 and unusually pointed at one end. 



The measurements of 16 eggs average 22.1 by 16.0 milhmeters; 

 the eggs showing the four extremes measure 23.4 by 15.7, 21.0 by 

 16.3, 21.0 by 16.3, and 23.3 by 15.3 millimeters. 



Young. — After 12 to 14 days of incubation the eggs hatch, producing 

 helpless young covered on the dorsal surfaces with sparse long 

 whitish down. At the approach of the parent bird, the gaping of the 

 young bird exposes the bright red Hning of the mouth contrasting 

 sharply with the yellow edge of the bill. As in incubation, the task 



