1921 BIRDS OF MONTANA 25 



foothill or sage-brush associations, the fir association apparently slowly en- 

 croaching upon the others. Tn such situations species of the different associa- 

 tions are to be found together. 



The Engelmann spruce association occurs mainly along the borders of moun- 

 tain streams, or on moist slopes where springs are abundant. (8ee fig. 8.) It 

 consists chiefly of spruce, with a small proportion of alpine fir, and west of the 

 divide, at low elevations, of lowland fir. It is mainly characteristic of the Cana- 

 dian zone, but occurs in some places in the Transition and in the lower Hudson- 

 ian, where the trees are stunted in growth and there is a greater mixture of 

 alpine fir. It forms the darkest and most dense of the coniferous forests, usually 

 Avith an undergrowth of small shrubs and of young spruce and fir. There are 

 three characteristic birds breeding in this association, the Western Winter Wren, 

 Rocky Mountain Creeper, and Golden-crowned Kinglet. I believe that the Sharjv 

 shinned Hawk and the Goshawk also breed in it in preference to other locations. 

 Most of the other mountain species that breed in both the Douglas fir and lodge- 

 pole pine associations are found in this one. 



The limber pine association occurs in limited areas in the northeastern 

 mountain region only, in the Transition foothills. It takes the place of the yellow 

 pine, found in similar situations farther south. It consists of an open grove of 

 misshapen and crooked trees, much like the white-bark pine of the Hudsonian 

 in appearance. The trees grow in this manner, however, more because of the 

 lack of moisture and the strong sweep of the winds, than because of the shortness 

 of the growing season. This association is inhabited by a mixture of mountain 

 and prairie species. No species is entirely characteristic, but the commonest 

 ones breeding in it are the Swainson Hawk, Red-shafted Flicker, Western AVood 

 Pewee, Clark Nutcracker, Pine Siskin, White-crowned and Gambel sparrows, 

 ^Montana Junco, Long-tailed Chickadee, Robin, and ^Mountain Bluebird. 



The arbor-vitae is another local association, found chiefly in moist situations 

 of low elevation in the northwestern mountain region. It consists of arbor-vitae, 

 mixed with spruce and lowland fir. It may be seen at its best about the shores 

 of Lake MacDonald and other lakes west of the divide in Glacier Park. The 

 birds breeding in it are mainly similar to those breeding in spruces, bat there 

 is also to be added to the list the Varied Thrush. 



Artificial associations are those formed by buildings, bridges, fences, plowed 

 fields, and various other men-wrought changes in the natural surroundings that 

 have an influence on the distribution of bird life. Such changes are the direct 

 causes of the scarcity or disappearance of certain species, of which the Long- 

 l)illed Curlew and Sage Hen are conspicuous examples in Montana. On the 

 other hand they cause certain other birds to be more abundant, by providing 

 nesting sites for them or supplies of food, where such did not exist before. With- 

 out attempting to classify artificial associations, I will merely name the species 

 dependent on them for nesting sites, with a mention of the sites chosen in cases 

 where it may not be obvious. These birds are: Killdeer (breeding in plowed 

 fields and along irrigation ditches), Red-shafted Flicker, Arkansas Kingbird, 

 Say Phoebe, English Sparrow, Purple Martin, Cliff, Barn and Tree swallows, 

 Dipper (breeding under bridges). House Wren, Robin, and ^lountain Blue])ird. 



