368 BULLETIN 196, UNITED STATES NATIONAL MUSEUM 



tures ever injure fruit or other crops. Their food is composed almost 

 exclusively of insects, which they hunt with untiring energy from 

 morning till night. Like the titmice and kinglets, gnatcatchers are 

 fitted by nature to perform a service which larger species are unable 

 to accomplish. There are hosts of minute insects, individually insig- 

 nificant but collectively a pest, that are too small to be attacked by 

 ordinary birds and are to be combated by man, if at all, only at great 

 expense. It is to so deal with such pests that they may not unduly 

 increase that these tiny birds would seem to be especially designed." 

 ^. The behavior, voice, and general habits are similar to those of the 

 eastern bird. It can be distinguished from the other California gnat- 

 catchers by having the outer tail feathers white for their entire length; 

 there is much less white in the tail of the plumbeous gnatcatcher, 

 and hardly any in the tail of the black-tailed; the gray of the upper- 

 parts is lighter in the western than in either of the others. California 

 jays have been known to destroy the nests of this gnatcatcher as well 

 as to rob them of eggs or young; and Mrs. Myers (1907) has seen the 

 little birds drive away a California shrike. 



Dr. Friedmann (1929) says that the western gnatcatcher is victim- 

 ized by the two western races of the cowbird, artemisiae and obscurus, 

 in much the same way as the blue-gray gnatcatcher is imposed upon 

 by the eastern cowbird. 



POLIOPTILA CAERULEA OBSCURA Ridgway 



SAN LUCAS GNATCATCHER 



HABITS 



As explained under the previous subspecies, this race of the blue- 

 gray gnatcatcher has been separated from the other western race on 

 the slight characters there mentioned. It is found only in southern 

 Lower California, from Cape San Lucas north to about latitude 28°, 

 where it is apparently resident. It probably does not differ materially 

 in any of its habits from the more northern form. William Brewster 

 (1902) says of it: 



The Western Gnatcatcher is a rather common resident of the Cape Region, 

 where it appears to be indifferent to conditions of mean temperatures or environ- 

 ment, for it occurs nearly everywhere from the seacoast (La Paz and San Jos6 

 del Cabo) to the summits of the highest mountains (Sierra de la Laguna). Mr. 

 Frazar found it breeding at San Jos6 del Rancho in July. His first nest, dis- 

 covered on the 7th, contained four eggs on the point of hatching, and was not 

 disturbed. Two others, taken respectively on the 14th and 19th of the month, 

 had full sets of four eggs each, all freshly laid. One of these nests, built in the 

 fork of a bush at a height of about five feet, measures as follows: Greatest external 

 diameter, 2.25; greatest external depth, 2.00; internal diameter at top, 1.30; 

 internal depth, 1.10; greatest thickness of walls, .50. The exterior is composed 

 of gray, hemp-like, vegetable fiber and narrow strips of reddish brown bark, and 



