Rufous-sided Towhee . The rufous-sided towhee is indicative of relatively 

 moist, lush shrub habitats, particularly those found in silver buffaloberry 

 coulees, riparian shrubbery, and the understory of riparian Cottonwood forests. 

 Sample abundances were thus greatest in the two routes having the highest repre- 

 sentation of those habitats -- the Missouri River and Prairie Elk routes -- and 

 the species was virtually absent from the habitats sampled by the Circle and 

 Flowing Well routes (figure 19). Sample abundances for each route were highest 

 in July, which probably corresponds to recruitment of young into the population. 

 Rufous-sided towhees are apparently present only during the period May through 

 September. The separation among routes is particularly clear for this species, 

 as is evident in figure 19. It is noteworthy that this species bred in a fair- 

 ly high density of 40 pairs/km^ (104 pairs per ten square miles) on the rela- 

 tively mesic silver buffaloberry-red osier dogwood census grid but not on the 

 drier, more open silver buffaloberry-silver sagebrush grid. Sample abundances 

 were significantly and positively correlated with trees and tall shrubs, horizon- 

 tal juniper (p<.001) and silver sagebrush (p<.01) and were significantly and 

 negatively correlated with grassland (p<.001). 



Lark Bunting . Large flocks of this species arrived in the study area in 

 May, and concentrated in the grassland and cultivated habitats found along the 

 Circle route (figure 20). Of particular interest was the observance of a male 

 in full breeding plumage near the Dreyer Ranch by two observers on March 10, 

 nearly two months before the normal arrival date. By June, the species had 

 shifted to its preferred breeding habitat -- grassland with scattered big or 

 silver sagebrush plants -- and was much more evenly distributed among the five 

 routes. Sample abundances declined gradually until September, by which time the 

 birds had left the study area. 



Vesper Sparrow . Sample abundance curves for the vesper sparrow are shown 

 in figure 21. Individuals of this common breeding species were most common in 

 big sagebrush shrubland habitats found along the Flowing Well and Prairie Elk 

 routes. They were surprisingly scarce on the silver sagebrush bird census grid. 

 The separation among the five routes is particularly clear for this species. 

 Most birds arrive in early April, and most are gone by August, but a few were 

 encountered on September runs. Sample abundances were significantly and pos- 

 itively correlated with big sagebrush badlands, little bluestem, and bluebunch 

 wheatgrass (p<.001), and were significantly and negatively correlated with cul- 

 tivation (p<.001), and tall shrubs and trees (p<.01). 



Brewer's Sparrow . The pattern of sample abundances for the Brewer's 

 Sparrow (figure 22) is remarkably similar to that of the lark bunting (figure 20), 

 except that the relative positions of the Circle and Flowing Well routes appear 

 reversed. Large numbers of Brewer's sparrows arrive in April and May, concen- 

 trating in the extensive big sagebrush scablands and shrublands found along the 

 Flowing Well route. Breeding activity reached a peak in May, and by June the 

 species had dispersed into the big sagebrush habitats along Prairie Elk Creek. 

 Singing activity was significantly and negatively correlated with time relative 

 to the start of the routes (p<.001); thus, low May species abundance values 

 for the Dreyer Ranch route are misleading, since the sagebrush habitats occurred 

 near the end of the route in May and near tiie beginning in June. Most birds were 

 gone by August. Two nests were found in silver sagebrush plants (table 10). 



85 



