594 ANIMAL LIFE IN THE YOSEMITE 



None was seen in early December and late February at either Pleasant 

 Valley or El Portal. 



During the early spring immediately after their arrival from the south, 

 the gnatcatchers are to be seen in pairs, the male in close attendance upon 

 the female. When the latter engages in the work of nest construction her 

 mate remains in the vicinity, part of the time accompanying her on trips 

 for building material or on foraging sorties. Otherwise he guards the 

 nesting precincts against invasion of any rival male. All the while, in 

 the heat of mid-afternoon as well as at other hours of the day, the male 

 gnatcatcher utters his fine wheezy song at frequent intervals, and the 

 female answers from time to time in similar tone of voice with single notes. 



When settled for nesting each pair of gnatcatchers is strongly localized. 

 Each keeps within a radius of not more than a hundred yards from the 

 nest tree. This localization permits an observer to take a more accurate 

 census of nesting pairs than is possible with many other birds. At Black 's 

 Creek, near Coulterville, our own counts led to an estimate of 64 breeding 

 pairs of the Western Gnatcatcher to each square mile in that immediate 

 district. Carrying these figures farther, in consideration of the estimated 

 area of the Upper Sonoran Zone included in our Yosemite section, we find 

 a total gnatcatcher population just before the appearance of the new 

 broods, to consist of 50,000 individuals. 



On the hills near Lagrange in early May, 1919, we found the Western 

 Gnatcatchers busily engaged in building their nests in the blue oaks. One 

 nest, complete but without eggs, found on May 8, may be regarded as 

 typical for the species. It was situated about 10 feet above the ground 

 near the periphery of the tree, amid small twigs and branchlets, and rested 

 directly on a horizontal branch about 40 millimeters in diameter. Outside, 

 it measured 80 millimeters in diameter and 45 millimeters in height ; the 

 cavity inside was 35 millimeters across — ^just the diameter to admit snugly 

 the body of the brooding bird. 



The nests are of deep cup-shape, and are constructed throughout of 

 light-weight materials. A framework of fine grass stems forms the main 

 wall, and this is covered both inside and out with softer substances. The 

 outside is felted with lichens such as abound on the bark of blue oaks, with 

 a few grass seed hulls, some small oak leaves, and occasionally a feather 

 or two, the whole being held together with spider web. The inside of the 

 nest is lined almost entirely with feathers, laid flat-ways of the inner sur- 

 face. Whatever the purpose of the bird in constructing such a nest, the 

 form and outside appearance are usually such that the structure might 

 easily be mistaken for a weathered stub or a small accumulation of debris. 



Other new nests were seen at Blacks Creek, west of Coulter\dlle, on 

 May 10 and 11, 1919. Some of these were on branches in situations similar 



