Spatial variation in densities of farmland birds in relation to pesticide use and avian food resources.
Since 1970, in a 62 km2 area of West Sussex, The Game Conservancy Trust has monitored autumn dispersion and productivity of Grey Partridges Perdix perdix, the abundance of invertebrates and plants in cereals in June, and the use of pesticides on crops. Locations of singing Corn Buntings Miliaria calandra and Skylarks Alauda arvensis within the study area are available from 1995-1997. Contours of smoothed bird density (male Grey Partridges, singing Corn Buntings and Skylarks) were constructed within a GlS. Grey Partridge density was negatively correlated with the average number of herbicide applications, as was skylark density, which was also negatively correlated with the average number of fungicide and insecticide applications. Both Skylark and Corn Bunting densities were positively related to an index of Grey Partridge chick-food abundance, and to the abundance of caterpillars in cereals. Grey Partridge chick survival rate was positively related to measures of weed abundance and diversity in cereals, and to the chick food index and abundance of caterpillars.