Summary 1.Fields left fallow after harvest (i.e. stubble fields) support high wintering densities of many species of granivorous bird. We examined correlates of use by eight such species of different types of intensively managed wheat and barley stubble fields, organic wheat fields and set-aside fields on mixed lowland farmland in central England. Field occupancy was studied in relation to the physical characteristics of fields and seed abundance. 2. Higher seed abundance was associated with greater occupancy by linnet Carduelis cannabina, grey partridge Perdix perdix, chaffinch Fringilla coelebs, yellowhammer Emberiza citrinella, reed bunting Emberiza schoeniclus and corn bunting Miliaria calandra. Larger areas of bare earth within stubble fields were associated with greater occupancy by linnet, yellowhammer, reed bunting and corn bunting, but lower occupancy by woodpigeon Columba palumbus. 3. On conventional intensively farmed sites, seed abundance and area of bare earth were significantly greater on barley stubbles than on wheat stubbles. 4. Seed numbers fell throughout the winter in all stubble types, although reductions were greatest on intensive barley stubbles, intermediate on intensive wheat stubble and lowest on undersown organic wheat stubbles. 5. Within fields occupied by linnets, areas used for feeding had significantly greater quantities of seeds known to be important in their diet. Feeding areas also had a greater area of bare earth than randomly selected 'non-feeding areas'. 6. Linnets and reed buntings were rarely found on fields where densities of weed seeds important in their diets fell below 250 seeds m −2 . In autumn, yellowhammers and grey partridges rarely fed on fields where cereal grain density was below 50 m −2 . However, in spring, both species fed on these fields irrespective of grain density, perhaps indicating a switch to other food sources. 7. We suggest that land managers wishing to maximize the value of overwinter stubble fields for granivorous birds locate such fields where there is a substantial natural regeneration of weed flora and where previous cropping (e.g. barley) is likely to offer a sparse stubble with substantial areas of bare ground.

Summary 1.The habitat use and diet of skylarks wintering on lowland farms were studied to assess whether changes in agricultural practice could have reduced their most favoured wintering habitats or foods. Faecal samples were collected and soil seed densities were estimated. Skylarks in 122 cereal stubble fields in Oxfordshire were counted monthly to examine habitat use. 2. Cereal stubble fields were more likely to be occupied than other crops, and densities of birds in occupied fields were high. Barley stubbles were significantly more likely to be occupied than wheat stubbles. Growing cereals were weakly selected. Sugar beet stubbles held high densities of birds. Rotational set-aside was occupied more frequently and held higher densities than non-rotational set-aside. 3. Field size affected field occupancy independently of crop type, with larger fields more likely to be occupied. Fields enclosed by hedges or trees tended to be avoided. Cereal and set-aside fields that were occupied by skylarks in at least 1 month held significantly higher soil seed densities than fields that were not occupied. 4. Differences in occupancy between crops could be explained by diet. Birds in cereal stubbles fed largely on cereal grain, whereas those in winter cereals fed largely on cereal leaves. Broad-leaved weed leaves were strongly selected as food in cereal crops and farmland grass fields. In grass fields, the proportion of the diet made up by broad-leaved weeds was positively correlated with their availability. Broad-leaved weed seeds did not make up a significant dietary component in any crop. 5. Our results show that the shift from spring to autumn sowing of cereals has led to a loss of the skylark's most strongly selected wintering habitat and best food source. In winter cereals and in grass there was a high selectivity for relatively scarce, and probably declining, food resources. Our results suggest that the retention of weed-rich cereal (particularly barley) and sugar beet stubbles through the winter, particularly in large open blocks, will improve conditions for skylarks in winter. Whole-field rotational setaside, particularly as naturally regenerating cereal stubbles, provides good winter food resources for skylarks.

Agricultural intensification is believed to have driven declines of farmland bird populations and the invertebrates and weeds on which they feed. We investigated whether habitat and weather, as surrogates for food availability, influenced nestling growth rates and condition of four farmland passerines (Skylark Alauda arvensis , Chaffinch Fringilla coelebs , Linnet Carduelis cannabina and Yellowhammer Emberiza citrinella ). We also tested whether nestling growth rates or condition influenced whether a brood subsequently fledged, starved or was depredated. Linnet nestlings are fed almost exclusively on seeds, and were unaffected by weather. Nestlings of the other species are fed mainly invertebrates and were affected negatively by rain but positively by increasing minimum temperatures and daily hours of sunshine. Condition and growth rates of Linnet nestlings were lower in nests further from oilseed-rape fields, rape seeds being important in the diet of this species. Nestlings of the other three species were unaffected by availability of habitats selected by parents foraging for nestling food. Brood fate was not influenced by growth rates or condition for any species. Most models explained little variation in the response variable. Possible reasons, including the possibility that parents trade off their own survival prospects to ensure reproductive success, are discussed.

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