WESTERN GNATCATCHER 365 



the river valleys. In the Lassen Peak region, according to Grinnell, 

 Dixon, and Linsdale (1930), "willow, valley oak, manzanita, digger 

 pine, blue oak, and buckbrush are all plants in which individul 

 gnatcatchers were seen. However, the portion of the section most 

 favorable for this bird, as indicated by concentration of breeding birds 

 to cover practically the whole of such area, was the tract of blue- 

 oak-covered hills north of Red Bluff and west of the Sacramento 

 River. There the park-like arrangement of the trees, each with many 

 slender branches covered with copious foliage, and with the inter- 

 vening spaces between the trees of a uniformly short distance, seemed 

 ideally to fulfill the requirements of this bud for nesting and foraging 

 activities." 



In Arizona we found this gnatcatcher only fairly common in the 

 foothills of the Huachuca and Dragoon Mountains and in the wider, 

 lower portions of some of the larger canyons, mainly between 5,000 

 and 6,000 feet, but never out on the lower plains or at higher eleva- 

 tions in the mountains among the coniferous forests. Some of the 

 foothills where we found the gnatcatchers were dotted with small 

 black-jack oaks, with more or less even, open spaces between them, 

 covered with mountain-misery and various other shrubs. A typical 

 canyon haunt was in Miller Canyon in the Huachucas. This was 

 heavily wooded along the stream with a row of big sycamores, ashes, 

 walnuts, maples, and cedars; at its wide mouth was an open, parklike 

 forest of large black-jack oaks in which numerous Arizona jays were 

 nesting; farther up the canyon were smaller oaks of various kinds, 

 madrones, manzanitas, and thickets of various kinds of shrubs. The 

 gnatcatchers seemed to prefer the smaller oaks. 



Territory. — In densely populated areas western gnatcatchers seem 

 to establish and maintain fairly definite breeding territories. Grin- 

 nell and Storer (1924) write: 



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 immedate district. Carrying these figures further, 

 in consideration of the estimated area of the Upper Sonoran Zone included in our 



