Diversifying crop rotations with temporary grasslands - Université de ...

Newton, 2004). Several bird species probably need both grasslands and arable crops for
breeding and feeding and thus suffered from the loss of mixed farming and the geographical
separation of crop and livestock production (Evans, 1996; Robinson et al., 2001; Moreira et
al., 2005). Weeds and invertebrates are both very important in the diets of many farmland
birds. Some birds probably suffered from a reduced presence of weed plants and invertebrates
to feed their chicks in spring and summer. Moreover, weed seeds are particularly important for
overwinter survival of adult farmland birds (Wilson et al., 1999; Vickery et al., 2001;
Robinson and Sutherland, 2002; Hawes et al., 2003; Marshall et al., 2003; Holland et al.,
2006; Siriwardena et al., 2006). Farmland birds clearly prefer fields with high weed seed
densities as illustrated in Fig. 2.
Fig. 2: Relation between weed seed density and skylark (Alauda arvensis) density in winter (Norfolk, UK).
Figure reproduced with permission from Watkinson et al. (2000).
During the last century, the weed seed offer was probably strongly reduced due to steep
reductions in weed seed bank densities (Robinson and Sutherland, 2002, see Fig. 3). Another
important reason was probably the reduction of untilled stubble fields where weed seeds stay
available on the soil surface during winter (Moorcroft et al., 2002; Gillings et al., 2005;
Moreira et al., 2005). The replacement of spring-sown crops by autumn-sown crops
contributed to the decline in the areas of untilled stubble fields during winter.
8