1100 U.S. NATIONAL MUSEUM BULLETIN 237 part 2 



exhibiting the general plumage of the southern and the field charac- 

 ters, lost in study skins, of the northern groups. 



The gray-headed junco is the only junco known to breed in its pure 

 form in Colorado, Utah, and Nevada, with the minor exception of a 

 race of the Oregon junco, J. 0. thurberi, in extreme w^estern Nevada. 

 Pure, unmLxed Junco caniceps in the northern and western parts of its 

 range confines itself, even where junco habitat extends far beyond, 

 within the Umits of those three states. Practically all breeding 

 records from near those state lines and adjoining parts of California, 

 Idaho and Wyoming are of birds in populations mixed and interbreed- 

 ing with J. oreganus, either thurberi west or mearnsi north. Junco 

 habitat in southeastern Arizona and extreme southwestern New 

 Mexico is occupied by the similarly plumaged, but yellow-eyed, 

 northern subspecies of the Mexican junco (J. phaeonotus palliatus). 

 Here there is no intermixing of the gray-headed and its neighbor, 

 the breeding ranges of the two species being separated by hot desert, 

 although one point of separation is no wider than 37 miles. 



Habitut. — Miller (1941b) says of the habitat of J. c. caniceps: 



The spotted distribution of this junco must be emphasized. It inhabits for the 

 most part a series of mountaintop islands above 7000 feet in the arid Rocky 

 Mountain and Great Basin ranges. Associations in which it breeds include 

 coniferous forest types dominated either by spruce (Picea), Pseudotsuga, Pinus 

 contorta, Pinus ponderosa, Pinus flexilis, or fir (Abies). It also breeds in pure 

 stands of aspen (Populus tremuloides) and of mountain mahogany {Cercocarpus 

 ledifolius). Compared with Junco oreganus, it shows high tolerance for arid 

 forest and ground cover. It may occupy aspen groves where there is no surface 

 water within two to five miles of the nest site. Unshaded forest floor with the 

 ground poor in humus and nearly lacking in green plant cover is unsuitable for 

 breeding. 



While this subspecies has a high tolerance of arid conditions, its 

 tolerance of moisture also is high, as is indicated by three nests 

 R. B. Rockwell (1910) found June 16, 1910 at Columbine Lake, a 

 40-acre Canadian Life Zone lake in northern Colorado at 8,630 feet 

 elevation surrounded by "a dense growth of pine and spruce extending 

 in places to the water's edge." Of J. c. caniceps breeding in the 

 Uinta Basin in northeastern Utah, A. C. Twomey (1942) reports: 

 "The birds nested in all the mountains of the Basin from altitudes of 

 7,500 feet to timberline at 10,000 feet. Their range included the 

 Douglas fir, yellow pine, blue spnice, aspen, lodgepole pine and 

 Engelmann spruce-alpine fir forests." 



In southwestern Utah, according to W. H. Behle (1943), the 

 gray-headed junco occupies approximately the upper half of the 

 Transition Zone ponderosa pine belt, which occurs between 6,200 

 and 7,600 feet, and the lower two-thirds of the Canadian Zone blue 

 spruce, white fir, and aspen at 8,000 to 9,500 feet. Behle says: 



