Vol. 5, No. 9 
Page 3 
A continuous roadside census route covering 16 sections was tentatively es¬ 
tablished to facilitate the evaluation of the effects of future prairie chicken 
management programs on the abundance and distribution of cottontails. 
Use of the weight of the cottontail lens as an indicator of age is now a stan¬ 
dard practice. Techniques were developed this month for adjusting the lens histogram 
to remove bias in dating seasonal peaks of productivity caused by the continuously 
changing growth rate of the lens throughout the life of the rabbit. 
The most satisfactory histogram results when individual weights are first con¬ 
verted to ages using the equation: 
x = (68.7927 / 2.4890 - Log 10 y) - 41 
Here x = the age of the rabbit in days and y = the weight of the lens in mg. 
It has been common practice to use histograms based on weights of lenses tabu¬ 
lated by 10 mg. classes. Such data must be adjusted if seasonal aspects of production 
are to be properly presented. Because of the continuously changing growth rate of 
the cottontail lens, there is a different time span represented by each 10 mg. class 
in the unadjusted histogram, i.e., the time interval represented by the 70-80 mg. 
class is 10.6 days while the interval represented by the 170-180 mg. class is 28.4 
days. A conversion table is given below. Classes are adjusted by dividing the 
number of lenses in each class by the appropriate correction factor. 
Table 3. —Correction factors for adjusting frequencies of weights of cottontail 
lenses tabulated by 10 mg. classes for histogram presentation. 
Weight Classes 
(mg) 
Correction 
Factors 
Weight Classes 
(mg) 
Correction 
Factor s 
20-30 
10.1 
120-130 
15.5 
30-40 
9.6 
130-140 
17.2 
40-50 
9.5 
140-150 
19.3 
50-60 
9.7 
150-160 
21.4 
60-70 
10.0 
160-170 
24.5 
70-80 
10.6 
170-180 
28.4 
80-90 
11.2 
180-190 
32.9 
90-100 
12.1 
190-200 
39.0 
100-110 
13.0 
200-210 
46.5 
110-120 
14.2 
Due to variability in lens growth rates among rabbits, it is suggested that 
estimating individual ages in days be limited to young of the year, i.e., those 
having lenses weighing less than 210 mg. 
I 
