Vol. 15 , No* 4 
Page 2 
cock-hen pairs along the audio-census routes near the listening stops indicated 
that these paired males, accompanied by their mates, did not whistle. It was 
believed that the majority of cocks whistling during the period from late May to 
mid-July were those whose mates were tending nests—probably incubating. This 
contention was supported by data obtained from juveniles (ages determined by 
wing molt) in the harvests. The bulk of the juveniles harvested during the 
first 7 days of each hunting season were from nests that were incubated from 
the first week of June to the third week of July. 
Responses of Prairie Chickens to Habitat Manipulation R. L. Westemeier, 
D. R. Vance 
As in the past nine springs, booming ground surveys were conducted this 
spring (1972) on the Bogota Study Area at no less than weekly intervals from 
mid-March through mid-April. These data were supplemented by observations 
recorded almost daily by visitors in blinds on several booming grounds. Counts 
were made during the first 1.5 hours after daybreak, and an effort was made to 
determine the maximum number of cocks on the area. 
The peak count of 196 cocks at Bogota this spring was 23 percent higher 
than the peak count in the spring of 1971 and represents the fourth consecutive 
increase in the Bogota flocks(s). The count this spring is 151 percent higher 
than the count made in 1963, when this census was initiated, and 430 percent 
higher than the low count of 1 968 - 
Except for two minor booming grounds involving only one or two cocks 
each, all booming was located on or within 200 yards of the sanctuaries. The 
traditional central core of the Bogota Area contained the phenomenal density of 
135 cocks—a half-section area containing the Ralph E. Yeatter, Marshall Field 
III, and Max McGraw sanctuaries (232 acres). Between the springs of 1971 and 
1972, the counts on the Otis and Fuson Farm sanctuary on the west edge of the 
area increased by 50 percent and the counts on the Mark sanctuaries on the 
northeast corner of the study area increased 57 percent. For the first time 
since its acquisition in 1965 , one cock was present regularly on the 80-acre 
Jamerson McCormack Sanctuary on the extreme south edge of the area. One 
morning four hens were seen with this vanguard. 
