BOCK WEEN 551 



descending to lower levels or going south to the deserts; the numbers in 

 the foothills, too, at this season become small. 



The Rock Wren seems to be totally unaffected by conditions of tem- 

 perature or humidity and is as much at home in the summer heat of the 

 San Joaquin Valley as in the cool and rarified air of North Dome or 

 Ragged Peak. The highest point at which it was seen was in Mono Pass, 

 at about 10,500 feet altitude. Another high place of observation was near 

 Vogelsang Lake, 10,350 feet. The species was observed in Yosemite Valley 

 on August 31, 1917 (Mailliard, 1918, p. 19). 



While in general features of structure and behavior a true wren, the 

 Rock Wren presents some peculiarities which clearly adapt it to its par- 

 ticular kind of environment. In shape of body and head it is notably 

 flattened, a feature which enables it to creep far into horizontal fissures 

 and into crevices between boulders; the bill is very long and slender, 

 enabling the bird to reach still farther, into remote niches, in its search 

 for an insect or spider; the legs are short, but the sharp-clawed toes are 

 very long, and have a wide span so that the bird can cling firmly to the 

 vertical or even beetling rock wall; the coloration, in toto, is that of the 

 average bare rock ; when the bird is examined at close range the indistinct 

 fine pattern of white and dusky dots and bars is seen to resemble, to a 

 suggestive degree, the minute patterning of the rocks. 



In size the Rock Wren is the largest of the wrens in the Yosemite avi- 

 fauna, being more than half again the bulk of the next smaller, the Canon 

 Wren. From that species, which often occurs in the same territory as 

 the Rock Wren, the latter may be known by its much paler coloration, 

 lack of contrast in color of throat and rest of body, and by its longer, 

 black-and-light-banded tail. The voices of the two are totally different. 



In the lowland and foothill country, where birds in general are 

 abundant, the Rock Wren might be easily overlooked through one's atten- 

 tion being absorbed by other species ; but in the high mountains, especially 

 on the granite domes and the heaps of slide rock where living things are 

 much scarcer, this bird comes more readily to notice. 



Like all wrens this bird is constantly on the move, turning to one side 

 or the other at short intervals. It also bobs its body down and up spas- 

 modically, in the manner of the Caiion Wren or of the American Dipper. 

 When it is perched on a point of rock its repeated movements often carry 

 it through a complete revolution in the course of a few seconds. During 

 this turning and bobbing its short clear trills are uttered, and in spring 

 its song is given. 



The song is not set in character, being a series of syllables, repeated 

 in irregular sequence, the successive series separated by short rests. One 

 bird observed near Pleasant Valley sang 4 to 7 notes at a time, the intervals 



