DOI: 10.5061/dryad.g4t3s
title: Data from: The influence of crop tiller density on the breeding performance of a cereal-nesting specialist

description: In the pursuit of maximizing agricultural yields and profits, crop
 management under intensive agriculture has reduced the heterogeneity of
 crop sward structure within fields. Several farmland bird specialists that
 nest within arable crops have undergone marked population declines during
 recent periods of agricultural intensification. Understanding the
 mechanisms that link crop sward structure to demographic fitness and
 population change may be important for developing effective conservation
 solutions. We studied whole-season breeding performance of a declining
 cereal crop specialist, the corn bunting Emberiza calandra, to test the
 relationships between crop sward structure and both nest site selection
 and reproductive output within intensively farmed landscapes. Experimental
 double-drilling of cereal seed was used to manipulate crop sward structure
 and explain the observed within-field nest distribution. The density of
 crop tillers (reproductive cereal stems) was a strong predictor of nest
 site selection and a disproportionate number of nests occurred close to
 (15–30 m) crop edges where regular seed sowing overlaps (operational
 double-drilling) occurred during crop establishment. Nest survival was
 subject to a strong crop edge effect and re-nesting rate increased with
 mean tiller density in the surrounding crop. Experimental double-drilling
 that simulated seed sowing overlaps increased crop tiller density (by 25%)
 and corn bunting nest density (by 406%) compared to adjacent areas of
 operational double-drilling. Corn buntings breeding in intensively managed
 cereal crops therefore place their nests in areas of high tiller density
 which under normal sowing practice tend to occur close to crop edges where
 nest survival is low. A simple population model indicated that
 productivity under conventional, intensive cereal management may be too
 low to sustain local populations in the absence of immigration. Modern
 cereal husbandry therefore creates an ecological trap for nesting corn
 buntings. Synthesis and applications. This study highlights a novel
 mechanism by which modern cereal crop management lowers the potential
 reproductive success of a conservation priority species nesting in
 intensively managed cereal crops. Unavoidable overlapping of cereal seed
 along crop headlands, close to crop edges, systematically produces patches
 of dense sward that attract nesting corn buntings. This creates an
 ecological trap because nests close to crop edges are subject to high
 predation rates, and this may be linked to the loss of arable weeds
 elsewhere within crops. When double-drilled strips are intentionally
 provided adjacent to these areas, nesting preference switches to these
 strips, suggesting a potential conservation solution. Provision of
 mid-field double-drilled strips at least 100 m from crop edges, if
 similarly selected by nesting females, should raise nest survival rates
 and improve population trends. Such interventions are simple and cheap to
 implement, unlike most conservation measures in high-value cropping
 systems.
description: ExperimentalNestDensity_DataThis file contains the data used in nest density analyses - experimental swards.A full description of the data is contained in the Readme sheet of the file.ExperimentalSward_QuadratData_NRateTreatmentThis file contains the quadrat-level sward data for the experimental sward nitrogen rate treatments. A full description of the data is contained in the Readme sheet of the fileExperimentalSward_QuadratData_SeedRateTreatmentThis file contains the quadrat-level sward data for the experimental sward seed rate treatments. A full description of the data is contained in the Readme sheet of the fileExperimentalSward_SubquadratData_NRateTreatmentThis file contains the subquadrat-level sward data for the experimental sward nitrogen rate treatments. A full description of the data is contained in the Readme sheet of the fileExperimentalSward_SubquadratData_SeedRateTreatmentThis file contains the subquadrat-level sward data for the experimental sward seed rate treatments. A full description of the data is contained in the Readme sheet of the fileModelInputDataThis file contains the input data for the population model. A full description of the data is contained in the Readme sheet of the fileNestSiteSelection_DataThis file contains the data used for nest site selection analyses. A full description of the data is contained in the Readme sheet of the fileNestSurvival_DataThis file contains the data used for nest, clutch and brood survival analyses. A full description of the data is contained in the Readme sheet of the fileRenesting_DataThis file contains the data used for re-nesting rate analyses. A full description of the data is contained in the Readme sheet of the file