Enhancing invertebrate food resources for skylarks in cereal ecosystems: how useful are in-crop agri-environment scheme management options?
UK agri-environment schemes rarely address within-crop biodiversity yet this habitat is used almost exclusively by some taxa. With the removal of set-aside, maximizing the ecological services provided by in-crop management options is critical. Field trials of small undrilled patches in the cropped area have been shown to increase skylark Alauda arvensis numbers and breeding productivity. This response may reflect a benefit for lower trophic levels, such as the invertebrates and arable plants on which birds feed. The technique has now been adopted as an option in the Environmental Stewardship scheme in England. Two within-field management techniques (undrilled patches and wide-spaced rows) were compared with standard row spacing on 10 conventionally managed farms growing winter wheat in northern and eastern England in 2002 and 2003. The effect of the treatments on invertebrate abundance, particularly invertebrates known to be important food for birds, was compared and the link between cover of arable weeds and invertebrate abundance was assessed. The diet of chicks located on the treatments was compared by faecal analysis. On a field scale, the treatments did not consistently increase invertebrate numbers. Invertebrates either colonized or avoided undrilled patches in the crop. The extent to which patches were colonized was dependent on vegetation cover, with the invertebrate assemblage structure responding strongly to broadleaved weed cover and, to a lesser extent, grass cover. The diet of skylark chicks did not differ between nests located in the two treatments. Synthesis and applications. Neither undrilled patches nor wide-spaced rows benefited invertebrate populations at the field scale. The value of undrilled patches for invertebrates would be enhanced by promoting weed cover, particularly broadleaved weeds; this could be achieved by creating the patches in the spring using cultivation and avoiding spraying with broad-spectrum herbicides. Higher numbers of non-pernicious weeds could provide food and refuge for invertebrates which are a food source for skylarks and other farmland birds that forage in the crop.