A survey design for monitoring butterflies

Abstract

A technique commonly used for surveying butterflies is the Pollard - Yates method (Pollard, 1977; Pollard and Yates, 1993). This method was originally developed for surveying butterflies at Monks Wood, UK (Pollard et al., 1975) and is now widely used in the UK. The method is based on a count of the number of butterflies seen along a fixed survey route. The Pollard - Yates method is easy to implement in the field but it does not allow for differences in the ability to detect butterflies among sites. Line transect sampling (Buckland et al., 1993) has similar survey methods to Pollard - Yates except that distance data is collected and used to estimate a detection function. Therefore, one of the main advantages of line transect sampling is that it provides estimates of abundance that are comparable among sites regardless of the sites' "butterfly-detectability". In addition, it can be used to derive unbiased estimates of local-site densities provided key assumptions are met (Brown and Boyce, 1996, 1998). We introduce some aspects of survey design for a monitoring scheme established for Karner blue butterflies (Lycaeides Melissa samuelis) in Wisconsin, USA.