Evaluating Point Count Efficiency Relative to Territory Mapping in Cropland Birds

Species richness, composition, and abundance of farmland birds were compared between point counts (50-m, 100-m, and 150-m radius half circles) and territory mapping on three 40-ha plots in Québec, Canada. Point counts of smaller radii tended to have larger density estimates than counts of larger radii. Territory mapping detected 10 species more than 150-m radius point counts. Territory mapping at 150-m radius detected more birds per species than point counts; relative abundances, however, were similar. Bird density is probably optimally estimated with a 100-m radius point count. After four visits, more than 80 percent of species and birds from 7 visits had been detected by 150-m radius point counts. Our modified point count method appears to be accurate enough to reflect the farmland avifauna characterized by more labor-intensive methods such as territory mapping. Several methods have been widely tested to estimate the number of birds in terrestrial habitats. Papers in Ralph and Scott (1981) give a broad overview of such methods and compare many of them. Territory mapping has usually been considered the standard technique against which most bird census methods have been compared (Anonymous 1970). Territory mapping is extensively used in Britain to monitor farmland avifauna (O'Connor and Shrubb 1986). In North America, territory mapping is used in the breeding bird census program to collect habitat specific information. The point count, or "Indice Ponctuel d'Abondance, IPA" method (Blondel and others 1970, 1977), has been widely used in Europe and North America. However, few attempts have been made to use it extensively in open landscapes. Within the larger framework of a Canadian Wildlife Service project to evaluate the impacts of agricultural practices on the avifauna (Rogers and Freemark 1991), a modified point count method was used to enable a larger number of plots to be surveyed (Freemark and Rogers, in this volume, Verner 1981). This paper compares species composition, richness, and abundance estimates of cropland point counts at varying survey distances. Territory mapping is used to provide complete census data for comparison.