Estimating Cottontail Abundance from Livetrapping Data

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Abstract
Estimates of cottontail (Sylvilagus floridanus) abundance were derived from several estimating equations applied to data obtained by livetrapping a confined population of known size on the Olentangy Wildlife Experiment Station, Delaware County, Ohio, in 1961. The same methods of estimation were also applied to field data obtained in 1963 at Robert Allerton Park, Monticello, Illinois. Findings suggested that probability of capture differed among members of the populations and, perhaps, changed after capture. The multiple census methods published in 1938 by Schnabel and in 1943 by Schumacher and Eschmeyer yielded estimates well below the numbers of rabbits in the populations. A method which utilized the frequency of capture, based on techniques of maximum likelihood estimation (MLE) for the Poisson distribution, also apparently tended to underestimate rabbit abundance. A simplified equation derived for MLE for the geometric distribution produced useful estimates and is suggested for estimating rabbit numbers from data obtained by livetrapping. Intercepts of linear regression lines fitted to logarithmic plots of data on frequency of capture also appeared to yield adequate approximations of the numbers of rabbits in the zero (uncaptured) class. The mathematical bases for using these methods are subject to limitations which are discussed.

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