Vol. 13, No. 2 
Page 4 
Grounds that are regularly used usually involve more than five or six cocks and 
the birds exhibit little temporal variation in their presence. The distinction 
between regularly used and uncertain status is made during the period when 
copulations are most commonly observed on the booming grounds. This period 
extends from late March through the first one-half of April in southern 
Illinois. 
On the 16-square mile study area at Bogota during the 7-year period of 
I 963 - 69 , distances between 49 booming grounds in both categories ranged from 
0.31 mile to I .56 miles, with a mean distance of 0.70+0.05 mile. Distances 
between 32 regularly used booming grounds were from 0.34 mile to 1.84 miles 
with a mean of 0.84+0.08, however, the means were not significantly different 
(P.^0.05). No correlation was found between the number of cocks using a 
booming ground and distances among booming grounds. Likewise, no correlation 
existed between the density of cocks on the study area and the mean distances 
among booming grounds during the 7~year period. 
These data, along with a consideration of (l) the preferred zone for 
nesting in relation to a booming ground (240 yards, MWRL 12(11) :2); (2) the 
optimum spacing among nests (120 yards, MWRL 12(2) :3); and (3) the optimum 
size of a field suitable for booming (10 acres, MWRL 12(6) :2) suggest that 
suitable sites for booming grounds should be spaced at distances of 600 yards 
on land that is available for prairie chicken management. 
6. Rabbit Management G. B. Rose 
The estimation of the energy metabolized by animals in the field has 
proven to be a difficult problem for ecologists, for although the energy 
metabolism of caged animals can be readily measured, the rate of metabolism 
of caged animals may be quite different from that of animals in the wild. 
However, it appears that the measurement of the energy utilization of animals 
in the wild can be approximated by measuring the food consumption of animals 
in large outdoor pens. If the efficiency of assimilation of the food is 
known, then the energy assimilated can be calculated from the energy consumed. 
Furthermore, if adult animals for which growth is zero are used, then energy 
assimilated equals energy metabolized. In this way the energy metabolized 
can be estimated. 
The amount of commercial rabbit chow eaten by six cottontail rabbits was 
measured during February, 1970. The outdoor pens in which the animals were 
kept were denuded of vegetation so that the rabbit chow was the only food 
consumed. 
The rabbits in the outdoor pens consumed an average of 103 grams of food 
per day, which, with a 63 percent assimilation efficiency, represents an 
energy assimilation of 260 kilogram calories (Kcal) per day. This figure is 
greater than the average of 210 Kcal per day assimilated by rabbits kept in 
outdoor cages or the average of 162 Kcal per day assimilated by rabbits kept 
in indoor cages. Thus, the difference between the 260 Kcal per day assimilated 
by the rabbits in the outdoor pens and the 210 Kcal per day assimilated by the 
rabbits in the outdoor cages may be assumed to be the result of the greater 
