MOUNTAIN CHICKADEE 579 



of labor is found upon examining in hand representatives of the two sexes 

 at this season. The breast and abdomen of the female are bare, the skin 

 rather rough-surfaced and thickened in the manner characteristic of incu- 

 bating birds generally ; while the male lacks any indication of such special 

 modifications. In the first part of the incubatory period the female may 

 flush from the nest when disturbed; but when the eggs are about ready 

 to hatch she will often remain upon them, even if the nest be chopped 

 open. She will then make a hissing sound and whir her wings in a remon- 

 strant manner from time to time whenever the disturbance becomes acute. 

 In one instance the female, fighting valiantly, maintained her place until 

 finally we picked her off from the eggs. In decided contrast is the behavior 

 of the male; he may come around at the beginning of the disturbance but 

 never exhibits much concern, and may wander away again after a little 

 while. After the young are hatched, both parents share equally in the 

 feeding of the brood. 



A most striking departure from the usual location for a chickadee's 

 nest was come upon in Yosemite Valley on June 23, 1920. A pair of the 

 birds had placed their nest far back in a crevice in the stone retaining 

 wall of the north approach to the new Sentinel Bridge. The entrance was 

 5 feet above ground, yet at the same time, 2 feet below the level of the 

 elevated roadway at that place. The young could be heard calling when- 

 ever a parent bird brought food. The rumbling of heavy vehicles overhead 

 did not seem to disturb the birds in the least. Choice of such an unique 

 site may have been prompted by the birds failing to find a nest location 

 of the usual sort in the neighborhood — a condition due to the removal of 

 dead trees by the Park authorities, and therefore, in final analysis, one 

 that was man-wrought. 



After the nesting season the chickadees and several others of the smaller 

 birds are wont to associate with one another in flocks of varying size. Such 

 a gathering was seen in Yosemite Valley on July 30, 1915. Included in 

 the openly formed yet coherent aggregation were the following species: 

 Mountain Chickadee, Black-throated Gray Warbler, Western Chipping 

 Sparrow, Sierra Creeper, Warbling Vireo, and Cassin Vireo. The birds 

 were foraging through black oaks, incense cedars, and young yellow pines, 

 each kind of bird of course adhering to its own particular niche and ovm 

 method of getting food. 



California Bush-tit. Psaltriparus minimus californicus Ridgway 



Field characters. — Size small, about one-third that of Junco ; tail longer than body. 

 Coloration plain gray, palest beneath; top of head inconspicuously brownish. No 

 contrasted marks anywhere. Habits somewhat like those of chickadee. Voice: A low 

 pst, pst, inflected variously under different conditions. 



