The potential value of managed cereal field margins as foraging habitats for farmland birds in the UK

Many farmland bird populations have exhibited marked declines in the last 20-30 years and there is growing evidence to link these declines to agricultural intensification. Field margin management is frequently proposed as a way of enhancing bird populations but there have been few attempts to assess the relative value of different management options. This paper aims to provide a preliminary assessment of the relative value of six different cereal field margin management practices in providing foraging habitats for farmland birds. It also briefly compares these with the benefits afforded by field and whole farm approaches such as set-aside and organic farming, to wildlife conservation on arable land. The field margins considered are: grass margins (separated into grass-only strips and grass/wildflower strips), naturally regenerated set-aside margins, uncropped wildlife strips, game cover crops and conservation headlands. Sympathetically managed field margins can provide a range of plant and invertebrate food resources for birds both in summer and winter. In general, the best winter food supplies (mainly seeds) will be provided by game cover crops and naturally regenerated rotational set-aside strips. The most abundant summer food supplies (invertebrates and seeds) will be provided by a diverse sward; grass/wildflower strips, uncropped wildlife strips and naturally regenerated rotational set-aside strips followed by conservation headlands. Field margin swards that are less diverse in terms of species composition and structural heterogeneity and that consequently support fewer invertebrates, can, nonetheless, provide higher quality foraging habitats for birds than an intensively managed crop up to the hedge base. A number of bird species such as yellowhammer (Emberiza citrinella) and tree sparrow (Passer montanus), prefer to forage in margins in winter and summer and many of the benefits of whole field approaches such as set-aside, overwinter stubbles and undersown cereals. could be gained from margins under the same management, Whole-field approaches are, however, required for boundary-avoiding species such as skylark (Alauda arvensis) and lapwing (Vanellus vanellus). Less is known about the use other birds make of margins, relative to their use of field centres in winter. Whole farm approaches such as organic farming, whilst being highly beneficial to birds, are likely to remain rather localised in the UK, whereas field margin management can be relatively easily incorporated into the farmed landscape on an extensive scale. (C) 2002 Published by Elsevier Science B.V.