366 BULLETIN 196, UNITED STATES NATIONAL MUSEUM 



Yosemite section, we find a total gnatcatcher population just before the appear- 

 ance of the new broods, to consist of 50,000 individuals. 



Nesting. — The same observers say that "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 flatways of the 

 inner surface. 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." 



They mention a typical nest in a blue oak as "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."' 

 Others were found "in crotches of small blue oaks, and several were 

 found in greasewood (chamisal) bushes, at a height of not more than 

 3 feet from the ground." 



It seems to be a characteristic habit of the western gnatcatcher to& 

 change the location of its nest once or twice before being sufficiently 

 satisfied with the site to finish the structure. Several observers have 

 reported that nesting material has been entirely removed from an 

 unfinished nest and used to build a nest in another location. This 

 may be because the birds saw that their nest had been discovered 

 and was unsafe for eggs or young; some birds are very sensitive to 

 human intrusion. Corydon Chamberlin (1901) says: "Of the first 

 few nests I saw being built none were finally occupied on their original 

 site. One pair near my camping place moved their nest and made 

 it over three times before being satisfied to deposit eggs in it. Each 

 time that the nest was nearly complete, the birds would discover a 

 more suitable site and then the work of tearing down would begin 

 and it would be moved piece-meal to the new place and until scarcely 

 a vestige of the nest remained in the old location. The third and 

 final resting place for this nest was in the main crotch of a small 

 white oak bush at such a height that I could just reach the nest by 

 standing on tip toe." 



He mentions several other nests, found in Tuolumne County, Calif., 

 one of which was "in the main crotch of an alder tree 30 feet from 

 the ground, the tree being in a creek bed." Another, 6 feet from the 

 ground on a small horizontal oak limb, "was made in between the 

 stub of a small twig and a live twig carrying a bunch of leaves that 

 hung over the nest like a parasol. 



