foraging and bark/bole drilling and gleaning. Species adapted to aerial capture 

 of insects (the sallying and soaring/swooping guilds) are present only during 

 spring and summer, when insects are abundant. The soaring/swooping guild, re- 

 presented largely by swallows and nighthawks, comprised 11% of all individuals 

 recorded during July. These birds were commonly seen in large, noisy flocks 

 around bridges and water areas, and are probably over-represented in the samples 

 due to their high detectabil ity. The number of aquatic species, which were pre- 

 dominantly migratory in the areas sampled, was greatest in spring and early sum- 

 mer; diving and mud-probing species were each represented by a single April or 

 May record. 



Seasonal Changes in Other Community Parameters . A number of descriptive 

 parameters were calculated for the bird communities sampled by the roadside sur- 

 vey technique. These parameters included, for each run and for the pooled monthly 

 totals of the four standard routes, bird species number, total number of individ- 

 ual birds, bird species diversity, bird species richness, bird species evenness, 

 single-species dominance, and two-species dominance. The values obtained are 

 shown graphically in figures 40 through 46. 



Bird species number for the four standard routes combined increased from a 

 low of 12 in January to a high of 66 in May (figure 40). The greatest increase 

 in species number occurred between the March and May runs. Species number re- 

 mained fairly constant throughout the breeding season (May through July), then 

 declined dramatically between the July and September runs. Much of the variation 

 in species number can be attributed to the arrival and departure of long-distance 

 migrants; however, breeding-season birds were not only more detectable but more 

 easily identifiable because of songs and displays. This undoubtedly tends to 

 exaggerate differences in species number between breeding season runs and the 

 April and August runs, when many breeding species were probably present but not 

 singing. The individual routes followed the same general pattern as that of the 

 pooled sample, except that peak species numbers were attained in June or July 

 rather than May. Note that, in nearly all months, the routes fall in the fol- 

 lowing sequence from lowest to highest species number: Flowing Well, Circle, 

 Dreyer Ranch, Prairie Elk, and Missouri River. The Missouri River route had the 

 highest species numbers of any route during all but the March and April runs, 

 when strong winds hampered detection of many species. 



Total numbers of individual birds recorded on the four standard routes com- 

 bined increased from a low of 379 in February to a high of 4143 in June (figure 

 37). Bird numbers apparently increased rapidly between the February and May runs, 

 but decreased more gradually between the June and December runs. Individual routes 

 also show a sharp breeding-season increase in bird numbers, again due partly to 

 increased singing activity (figure 41). The curve for the Circle route shows a 

 pronounced peak in September, largely attributable to a fall increase in horned 

 lark singing activity. The Flowing Well route had the fewest individual birds 

 recorded during most monthly runs. The sequence for the other routes is not clear. 



Seasonal changes in diversity (H') of the bird community samples are shown in 

 figure 42. This diversity index is determined in part by species number, so it is 

 not surprising that ttie curves in figure 40 are generally similar to those in 

 figure 42. Indeed, plots of the species richness component of the diversity index 

 (figure 43) are nearly identical in form to those of species number (figure 40). 



159 



