A Simple Population Estimate Based on Simulation for Capture-Recapture and Capture-Resight Data

The use of capture–resight data for population estimation has seldom been exploited. It offers potential flexibility and advantages to the design of biological investigations in which a population estimate is required. Presently, the Petersen model is the only method for estimating closed populations using capture—resight data. A simple Monte Carlo simulation method can lead to a full probability distribution for the population. From this probability distribution, one can compute maximum likelihood estimates and a likelihood interval on the population. The shape and asymmetry of the distribution and width of likelihood intervals are determined by sampling heterogeneity and sample size. The method is simple and can be used by anyone with access to a microcomputer. Since it is data—intensive, estimates based on small data sets (including capture—recapture) with few animals can be quickly calculated. The method is especially applicable to species and habitats in which capture–resight, radiotelemetry, or other tracking data can be obtained and to situations in which nonrandom catchability or sightability is likely after the initial capture. The technique successfully estimated populations of badgers, bison, and crested porcupines. We compare observed with theorectical sighting distributions to examine the effects of model and sampling biases.