Vo 1. 14, No. 2 
Page 4 
a third year after the first capture, and 3 a fourth year after the 
original capture. From these data a 1ife table was constructed, which 
shows mortality rates of 0.82 for the first to second year of recapture, 
and 0.77 for the second to third year of recapture, or an overall average 
mortality rate of 0.80. 
In a previous study, a survivorship curve was calculated based on 
weights of eye lenses of cottontail rabbits collected in Illinois. An 
average monthly mortality rate of 12.7 percent was computed, which 
represents an annual mortality rate of 80.4 percent. Thus, the 
estimated annual mortality rate in the earlier study, which applies to 
a somewhat younger group of rabbits (from 4 to 29 months) than those 
treated in this study, is essentially the same as the mortality rates 
estimated here (for rabbits 15 to 39 months of age —the youngest group — 
with some older than 51 months). 
In another, and later, study, it was estimated that the expected 
proportion of juveniles (age determined by the eye-lens or epiphyseal- 
closure techniques) in cottontail populations in the Midwest averaged 
0.83. Accordingly, the expected year-to-year mortality rate for 
juveniles would be 83 percent. This mortality rate for an.mals in the 
first year of life is little different from the mortality rates of 
adults, as determined from the trapping data. 
In the first study mentioned, the mortality data were obtained from 
rabbits collected mostly in east-central Illinois (Champaign, Piatt, 
McLean, and Ford counties), and some in southern Illinois. The estimate 
in the second study was based on rabbits harvested in Michigan, Ohio, 
Wisconsin, Illinois, and Missouri. Thus, the similarity of the 
mortality rate for rabbits on the 100-acre study area at Robert Allerton 
Park to these other rates that applied to much larger areas gives 
support to the belief that data derived from work on the Allerton area 
are representative of other areas in Illinois and the Midwest. This 
emphasizes the high annual mortality of adult as well as young-of-the- 
year cottontails throughout their range. 
