Modification of farming practice at field margins to encourage wildlife.

Abstract

Until recently, arable farmland has been largely ignored as a wildlife habitat by ecologists in favour of more diverse, but less extensive, ecosystems. As a result, the effects of the dramatic changes in farming practice which have occurred over the last decades upon farmland ecology, and upon the individual species adapted to live in this environment, have gone largely unrecorded, except for those species considered to be serious weeds or pests. An exception to this generalisation is the Grey Partridge, Perdix perdix, which has been the subject of a long-term study in southern England, known as the Partridge Survival Project (Potts and Vickerman, 1974; Potts, 1986). Data from the Game Conservancy's National Game Census have shown that this species has suffered an 80 per cent decline since 1952. Detailed monitoring of a 62km² study area in West Sussex since 1968, backed up by experiments, has implicated increasing pesticide use as a major cause of this decline (Potts, 1986).

The pesticides were not directly toxic to partridges, but caused a reduction in numbers of the insects which form the major part of the diet of partridge chicks during their first few weeks of life. This has led to increased rates of chick mortality during this early phase when they are entirely dependent on insect food (Potts, 1986; Green et al., 1987). The activity of pesticides on chick-food items may be directly insecticidal (Vickerman and Sunderland, 1977; Sotherton et al., 1987; Sotherton and Moreby, 1988) or indirect, in the case of herbicides, by removal of the weed host plants of preferred chick-food insects (Southwood and Cross, 1969; Vickerman, 1974; Sotherton, 1982; Potts, 1986).

Broods of grey partridge chicks feed almost exclusively in cereals, and prefer the edges of fields (Green, 1984). From 1983 onwards, experiments have been carried out in which pesticide use has been modified over a 6m wide strip of crop at the edge of cereal fields. Greater numbers of preferred chick-food insects were found within these areas, with dramatic results in terms of improved grey partridge chick survival rates (Rands, 1985, 1986, in press; Sotherton et al., 1985). Survival rates of pheasant chicks, which are similarly dependent on insect food in early life (Hill, 1985), were also increased (Rands, 1986). The implementation of this technique over approximately half the cereal acreage on the main study area (25 per cent of the total farm area) over four years (1983-6), has brought about an increase in spring pair density of grey partridges from four to twelve pairs per km² (Rands, in press).