On the variable circular plot method of estimating animal density.

The development by ornithologists of the variable circular plot method of estimating bird densities from observer-to-bird distances has led to estimation problems similar to those of line transect sampling, but to apply line transect methods without modification requires that the distance data be transformed to areas by squaring. Application of line transect models to area data may lead to poor model performance and erroneous conclusions. Developments based on distance data are discussed, and binomial models are derived for the special case in which birds are categorised simply according to whether they are within or beyond a specified distance.-from Author