Vol. 8, No. 1 
Page 5 
Capture records from monthly 10-day trapping periods in October, November, 
December, and January provide a third method for calculating mortality. Only the 
65 cottontails handled during the ear 1y-October trapping period were used in these 
calculations. Of these, 18 were never caught again and 47 were recaptured during 
November, December or January. The indicated disappearance rate from October to 
November was 18 4- 65, or 28 percent. Some of the 18 rabbits which were never 
caught after October should have been alive in November even though they were not 
caught during that month. Therefore, the indicated disappearance rate should have 
exceeded the actual mortality rate. 
Ten of the 65 rabbits caught in October were not caught in November but were 
caught in either December or January. The disappearance rate from November to 
December was 30 percent. Therefore, we can estimate that 14 (10 4- 0.70) of the 
October-caught rabbits were alive but not captured during November. We can use 
this figure to adjust the October to November disappearance rate and obtain an 
estimate of October to November mortality. Four (14 - 10) of the 18 animals which 
disappeared after October are estimated to have been alive in November. The 
estimate of ear 1y-October to ear 1y-November mortality is therefore 14 4- 65, or 22 
percent. This supports the previous estimates of 23 percent mortality. 
It is concluded that this rabbit population declined by about 22 percent from 
October 5 to November 5 - and the opening day of the hunting season was still 19 
days away! (Preliminary estimates indicate that the total mortality from October 
5 to opening day was around 36 percent.) 
Recapture records indicate that mortality was greatest among the youngest 
rabbits. Table 2 indicates, by size-classes, the disappearance rates for rabbits 
caught in October. The disappearance rate for rabbits weighing less than 900 grams 
in early October was especially high. The disappearance rates for known-adults* 
and for rabbits weighing more than 1,300 grams in early October probably over¬ 
estimated the mortality in these groups since our data indicate that these rabbits 
have a low probability of capture. 
Lord, R. D., Jr. 1959* A method for measuring mortality of cottontail rabbits in 
winter. J. Wildl. Mgmt. 23(2):241-243. 
Table 2. Recapture records and disappearance rates for cottontail rabbits caught 
in October 1964 on the Allerton Park 4-H Area. 
Weight in Early 
October (grams) 
Number Caught, 
October 
Number 
Recaught, 
November 
or Later 
Disappear- 
ance Rate 
(percent) 
Number 
Recaught, 
December 
or Later 
Disappear- 
ance Rate 
(percent) 
Under 500 
3 
1 
67 
0 
100 
500 - 900 
8 
4 
50 
4 
50 
900 - 1,100 
9 
7 
22 
6 
33 
1,100 - 1,300 
21 
19 
10 
10 
52 
Over 1,300 
9 
6 
33 
6 
33 
Known-Adu1ts* 
15 
10 
33 
6 
60 
* Known-aduIts 
are animals which 
were captured 
and released 
on the 4-H 
Area during 
or prior to, the spring of 1964. 
