November 1949 9 16 7 21 December 1949 16 9 3 48 March 1950 11 9 3 33 April 1950 9 7 2 32 October 1950 9 3 3 9 November 1950 3 3 1 9 December 1950 3 7 3 7 January 1951 7 14 3 33 February 1951 14 7 4 25 March 1951 7 5 3 12 April 1951 5 6 3 10 November 1951 3 6 1 18 December 1951 6 5 1 30 January 1952 5 11 3 18 February 1952 11 13 4 36 March 1952 13 9 5 23 April 1952 9 3 1 27 Crude census-figures were obtained by utilizing the Lincoln Index and computing the total on the basis of the ratio of marked (and recognizable) individuals to others caught in a sampling period. A large number of census figures were obtained over the three-year period of the study. Each separate census, however, was based on an inadequate sample as the number of marked individuals taken at each sampling, as recaptures from the previous sampling period, varied from one to five. While little confidence can be placed in any one census computation, the trends of figures from series of such computations reveal the approximate number of opossums on the area if due allowance is made for certain distorting factors. Presumably the differences in figures obtained at different samplings result chiefly from the margin of error in the data, although it is true that there is rapid change in the actual number of opossums. The number of active opossums in the region of the study reaches a peak in late summer and early fall, when second litters of young have grown large enough to become independent. At this season the population contains a high proportion of young of the year. During the ensuing months of fall and winter there is a steady decrease in numbers, through various mortality factors, with no replacement until young are born about the first week of March. These young do not become independent until late May or early June, and during the intervening months there is a further reduction of the adults and yearlings, so that the active population reaches its annual low point in late spring. At that time of year most opossums are in poor physical condition.