The indirect impact of pesticides on farmland birds.

Abstract

In recent decades there has been growing concern that populations of many species of farmland birds are declining in Britain (O'Connor & Shrubb, 1986, Potts, 1986, Fuller et al. 1991, Fuller et al. 1996). This pattern is being repeated across Western Europe (Busche 1989 a, 1989 b, Tucker & Heath, 1994) and it is widely assumed that these declines are linked with the widespread intensification of agriculture, especially since the 1970s (Potts, 1991, Tucker & Heath, 1994, Fuller et al. 1996).
Results from the British Trust for Ornithology's Common Birds Census (Marchant et al. 1990) show that the declines for seven species during the 1970s and 1980s were more than 50%. These species are: Tree Sparrow (85% decline); Corn Bunting (76%); Grey Partridge (73%); Turtle Dove (72%); Reed Bunting (59%); Linnet (56%) and Skylark (54%). These dramatic declines in numbers are also associated with reductions in their range (Gibbons et al. 1993). Overall, a much greater proportion of farmland bird species is in decline than is the case for birds in any other habitat (Fuller et al. 1996, Potts,1991).
The Grey Partridge (Perdix perdix) has been called 'the barometer of countryside change' because it is an excellent indicator species for the habitat quality of farmland (Potts 1986). As agriculture intensified partridge numbers declined (by 83% according to Potts 1986). Intensification has involved many processes involving both cropped and non-cropped habitats on the farm. These include increasing field size (hedgerow removal), increased use of fertilisers, improved plant breeding, and the increased use of pesticides. Since the 1950s, both increases in the number of pesticides used (Table 1) and increases in the areas of cereals sprayed (Table 2) have occurred.