9 
Rabbit Management 
Vol. 8, No. II 
Page 5 
J. A. Bailey, R. J. Siglin 
6 . 
The annual fall census of cottontail rabbits on the Allerton Park 4-H Area 
was conducted November 20, I 965 , with the aid of wildlife management students of 
the University of Illinois. 
The tails of 33 rabbits were dyed yellow with picric acid during early October. 
The tails of 34 other rabbits were dyed with rhodamine B, a red pigment, during 
early November. The drive conducted November 20 produced 132 observations of 
cottontails: 15 white tails, 44 yellow tails, and 73 red tails. Population 
estimates and confidence limits applicable to early October and to early November 
can be calculated using the well-known Lincoln-Peterson index method. 
It is estimated with 95 percent confidence that there were 99-24 rabbits on 
the 4-H Area in early October and 61tl0 rabbits in early November. If the two 
marked segments of the population are combined, it can be estimated with 95 percent 
confidence that there were 76t5 rabbits on the 4-H Area in late October. 
The indicated mortality from early October to early November is 38 per 99> °r 
38 percent. This mortality estimate is supported by another estimate of mortality 
based upon data concerning only the yellow-tailed rabbits. The drive indicated 
that one-third of the cottontails had yellow tails. It is therefore estimated that 
one-third of 61, or 20 yellow-tailed rabbits, were alive in early November. The 
indicated mortality of yel1ow-tai1ed rabbits is therefore 33 less 20 per 33» or 
39 percent. 
Ten years of data on the cottontail population of the 4-H Area are presented 
in Table 3* 
Table 3- Estimates of cottontail rabbit abundance on the Allerton Park 4-H Area, 
1956-65. 
Year 
Sprinq Population 
Fa 1 1 
Population 
March 
Early October 
Early November 
1956 
• — - 
333 
— 
1957 
47 
259 
— 
1958 
31 
324 
— 
1959 
132 
239 
— 
i960 
56 
309 
— 
1961 
161 
363 
— 
1962 
24 
107 
— 
1963 
61 
— 
132 
1964 
58 
132 
101 
1965 
— 
99 
61 
This population crashed in 1962 and has never recovered. The 1965 fall 
population estimates are the lowest on record. The 10-year decline in the number 
of rabbits present on the 4-H Area has been associated with habitat changes 
related to plant succession (Monthly Wildlife f.esearch Letter, May, 1965). 
9 
