Effects of the proportion and spatial arrangement of un-cropped land on breeding bird abundance in arable rotations

1. The response of bird abundance to the proportional availability of un-cropped land (i.e. land that could be cultivated, such as fallows, grassflower or wild bird areas) is under-studied but of considerable significance for managing declining populations on farmland in western Europe. 2. In this study, bird abundance was examined at a scale consistent with many national monitoring schemes. Birds were counted on 28 farm sites of c. 100 ha, representing cereal-based and organic rotations. Sites were surveyed in summer, from 2007 to 2010, to assess the effect of the percentage cover and spatial arrangement of un-cropped land on bird abundance, with data analysed at the whole-farm (not patch) scale. 3. Un-cropped land area had significant effects on the abundance of key species (those with a high dependency on farmland) when controlling for effects of semi-natural habitats and management. On farms with 10% area of un-cropped land. 4. Positive, significant effects of the percentage area of un-cropped land were detected for lapwing, skylark, linnet and yellowhammer and for all highly farmland-dependent species combined. The relationship between un-cropped land and bird abundance was stronger on conventional compared with organic farms, suggesting a greater importance of un-cropped land on conventional farms. 5. Un-cropped land patch arrangement was significant for skylark and linnet abundance but generally weak amongst species compared with the availability of un-cropped land. Skylarks were positively associated with a larger relative edge effect amongst patches, whereas linnets were more associated with larger blocks of contiguous habitat. 6. Synthesis and applications. This study provides important evidence for a proportionate effect of habitat provision on farmland bird abundance. The relative area of un-cropped land had the strongest effect on bird abundance. Sites with