Arable field margins managed for biodiversity conservation: A review of food resource provision for farmland birds

Most arable field margins are sown grass strips which are limited in the avian food resources they offer but potentially supply grass seeds and, depending on the complexity of the sward structure, a range of arthropods. Adding perennial forbs to a grass mixture provides more diverse plant and invertebrate food resources for birds. The availability of seeds and invertebrates on uncropped margins is strongly influenced by management, particularly Cutting, cultivation and herbicide use. Cropped margins with reduced chemical inputs and wild bird cover crops can provide relatively high food resources compared with a conventionally managed crop. However, resources are only present until harvest, their plant communities are relatively poor and arthropod abundance is usually lower than in uncropped margins. The best winter food supplies for birds will be provided by options that create seed-rich habitats in winter. The best summer food supplies will be provided by options that create a structurally and floristically diverse sward. The least valuable margin in terms of food resources is a grass-only strip. On an area-for-area basis, field margins will potentially produce food resources for birds more cost-effectively than whole farm practices such as organic farming, though the value of margins will depend on their management and the diversity of margin types at a farm scale. Because no single margin type can provide the optimum year-round food supply, different types of margins should be incorporated at the farm level, but appropriate management (and further innovation in margin design) is needed to deliver their benefits. Field margins should be managed in conjunction with adjacent boundary features, especially hedgerows, to create complex structures that maximise nesting opportunities for birds and create habitats for a range of invertebrates. (C) 2009 Published by Elsevier B.V