Methods for estimating wild animal populations are among the most important techniques needed in wildlife research. This paper describes the results of using two census methods (plus a variation of the methods) simultaneously on two small, intensively studied woodlots. Comparison of these results discloses their practicality in censusing squirrels. This study was conducted over a period of 3 years, 1952-55, in two 10-acre woodlots on the grounds of a hospital on the outskirts of Baltimore, Maryland. These woodlots were stands of large mixed hardwoods, with some individual trees up to 4 feet in diameter, and appeared to be excellent squirrel habitat. Each woodlot was relatively isolated from other woodlots, and movements to and from other forested areas were therefore restricted. The best applicable method for estimating squirrel populations appeared to be one based on some type of mark and recapture ratio, especially since animals had to be captured and marked for the study of their social behavior and movements (Flyger, 1955). In addition to trapping squirrels, observations were made on squirrel activity in the woods, permitting counts to be made of the number of animals seen per unit of area. These population estimates, using trap-recapture data and number of animals seen per unit of area, were made at the same time and involved the same squirrels. Comparing the results of these estimates (Table 1) reflects some of the characteristics and limitations of each method.
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Vagn Flyger (1959) studied this question.