A quick method for estimating butterfly numbers during surveys

This paper describes how the size of butterfly populations may be quickly assessed during surveys. The method is a development of Pollard's transect technique, which measures changes in adult numbers in time on fixed sites. In this development, comparability between counts made in the same season on different sites is achieved by ensuring that the transect representatively samples each population, and that the results take account of the length of transect, size of site, and the recording date. The accuracy and usefulness of the method are assessed, using examples taken from six recent surveys. It is concluded that the method gives an accurate measurement of numbers for species that fly freely in open habitats, and an adequate, but less accurate, estimate for species that aggregate or fly in heterogeneous habitats.