Vol. 9, No. I 
Page 6 
Table 5- Important grass 
(both sexes) on 10 census 
land acreages per section 
areas in southeastern 111 
and numbers 
inois. 
of prairie chickens 
1963 
1964 
1965 
Undisturbed grassland and 
grass hay per section 
41 .6 
36.4 
16.5 
Pra i rie chickens on 
booming grounds* 
311 
288 
189 
Prairie chickens 
per section* 
2.6 
2.4 
1 .6 
* In 1964 and 1965, 12.5 percent and 13-8 percent, respectively, of the total 
counts were hens. 
6. Rabbit Management J- A. Bailey, R. J. Siglin 
Investigators in Missouri have described ulcerative enteritis as a disease in 
the cottontail rabbit. The disease is believed to be a response to nonspecific 
stress and can be caused by crowding. Among its symptoms are profuse diarrhea, 
gastric ulcers, enlarged adrenals, and a small spleen. A disease of this nature, 
being related to intraspecific stress, could be important in regulating population 
density. 
A condition index, based upon the ratio of body weight to the cube of body 
length, is often used to evaluate the health and vigor of mammals. During 1965 
the relationship between a condition index and the occurrence of symptoms of 
ulcerative enteritis was investigated. Preliminary results are reported here. 
Thirty-one juvenile male cottontails were collected on the South Farm of the 
University of Illinois between June 23 and October 27, 1965- The animals were 
obtained by trapping and by hunting at night. The weight and total length of each 
animal were recorded. Total length was obtained by grasping the animal by the 
neck and hind legs, extending the animal, and measuring from the tip of the nose 
to the tip of the hind feet. The animals were frozen for later autopsy. Upon 
autopsy, the spleen and adrenals of each animal were weighed after removal of 
associated tissues and blotting on moist paper. A condition index, the ratio of 
body weight in grams to the cube of total length in decimeters, was calculated for 
each rabbit. An adrenal-spleen ratio, the average weight of adrenals divided by 
the weight of the spleen, was also calculated for each animal. The data are 
summarized in Table 6. 
A regression analysis indicated that condition indices were inversely 
correlated with adrenal-spleen ratios according to the formula Y = 5-75 • 2.5 +X, 
where Y = the condition index and X = the adrena1-spleen ratio. The coefficient 
of correlation, -0.49, was significant from zero at the 99 percent level of 
confidence. These results suggest that condition indices based upon external 
measurements can be used ; n evaluating the incidence of stress in cottontail popu- 
1 at ions. 
