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NATURALIST'S GUIDE TO THE AMERICAS 



cases burrow to much greater depths than 

 related species of other communities. 

 4. There is a predominance of hoppers 

 or fast walkers. The development of 

 hopping as a chief mode of progression 

 is not so much discouraged on the grass- 

 land as in several other formations by 

 frequent collisions with tall vegetation. 

 The habit of running is favored by bare 

 soil and is more marked among insects 

 of the drier than of the moister parts 

 of the grassland and still more among 

 those of the desert. 



Subdivisions of the grassland formation 



1. The Buffalo-grama grass or climax 

 grassland association. Nearly all the birds 

 of the i-egion nest usually or occasion- 

 ally in this association. The Sprague's 

 Pipit is here characteristic. The bison 

 and the pronghorned antelope appear 

 to have been at home here. The striped 

 gopher is most abundant here, but 

 reptiles and toads are less abundant. 



B. The Wheat Grass or Clay Grassland 

 Association. Few birds nest in the 

 wheat grass associations. The relative 

 barrenness of the upland areas and the 

 frequency of flooding of the other 

 portions are doubtless major deterrent 

 influences. The sharp-tailed grouse, 

 however, is more numerous in the flood- 

 plain phase of this association than 

 elsewhere, possibly because the taller 

 vegetation affords more protection than 

 the upland associations. Each prairie- 

 dog town has one or more broods of 

 burrowing owls. The prairie-dog is 

 the most conspicuous mammal. In 

 parts of this association, notably in 

 Custer and Fall River counties, nearly 

 every low terrace along the valleys is 

 occupied along much of its extent by 

 prairie-dog towns. The danger of being 

 drowned out by the flood waters is 

 greatly decreased by piling up around 

 each hole much of the dirt brought up 

 from below. Many entrances are as 

 much as 12 or 15 in. above the general 

 level of the "flat." This piling up is not 

 accidental, as is shown by the repeated 

 repairing by scraping dirt in from the 

 periphery of the mound, and by the fact 



that in areas not subject to frequent 

 flooding the detritus brought up from 

 below is scattered widely. The long- 

 tailed weasel and the black footed 

 ferret, which prey upon the prairie- 

 dog, are numerous, though not often 

 seen. Gophers and other burrowing 

 mammals are lacking in most of the 

 flood-plain areas in the gumbo region, 

 probably because of the floods. 



3. Bunch-grass or Dry-soil Steppe 

 Association (sand hills). Most of the 

 animal life of sandy regions is associated 

 with the springs and streams. The 

 areas occupied by the typical sandhill 

 vegetation have a sparse and not dis- 

 tinctive fauna so far as the larger ani- 

 mals are concerned. Of such typical 

 portions, the birds most abundant are 

 the western vesper sparrow, lark bunting 

 and the western meadowlark. Sandy 

 areas within the prairie region of San- 

 born County, eastern South Dakota 

 form eastern outliers of the breeding 

 range of the prairie sharp-tailed grouse. 

 The mammals most frequently seen are 

 the jackrabbit, the cottontail rabbit, 

 the plains chipmunk and the pocket- 

 gopher {Geomys lutescens). Because of 

 the relative wildness of rough, sandy 

 areas, they form retreats for wide 

 ranging mammals such as wolves and 

 coyotes. Of the reptiles, the most 

 abundant snake is the hog-nosed snake 

 {Heterodon nasicus). The yellow striped 

 swift (Cnemidophorus) is plentiful in 

 the more southern sandhills and another 

 lizard occurs, as does a land turtle 

 {Terrapene ornata). Several insects are 

 abundant in sandy areas, including 

 certain tiger beetles and the ant lion. 



4. Buckhush Association. There are 

 no large animals restricted to these 

 patches though there are many nests of 

 birds. In the grassland region, the 

 prairie sharp-tailed grouse, long-billed 

 curlew, upland plover, marsh and Swain- 

 son hawks and other large birds, as well 

 as western meadow-larks and Brewer 

 black birds often nest here. Cotton-tail 

 rabbits and ground-squirrel. {Citellus 

 tridecemlineatus, C. franklinii), and the 

 prairie vole {Microtus ochrogaster) are 



