Habitat selection by yellowhammers Emberiza citrinella on lowland farmland at two spatial scales: implications for conservation management

Yellowhammer Emberiza citrinella populations have declined rapidly in the UK over recent decades, and a clear understanding of their habitat requirements is important to help inform conservation schemes. We aimed to disentangle and rank the effects of winter versus breeding season habitat characteristics. 2. We used information theoretic methods to analyse the factors determining yellowhammer distribution across 26 sites in England and Wales. We did this at two spatial levels: individual field boundaries and individual territories, the latter consisting of spatialclusters of boundaries.3.We considered the role of nine predictor variables, all of which have been suggestedin the literature as potentially important. These comprised boundary height and width,and the presence of hedges, trees, ditches, boundary strips, tillage crops, winter set-asideand winter stubbles.4.The results of the statistical modelling showed that winter habitats play an importantrole in determining where birds locate territories in summer. In particular, the presenceof rotational set-aside fields in winter showed the strongest association with summerterritories.5.There were minor differences between the territory- and boundary-based models.Most notably, the territory data demonstrated a strong preference for territoriescontaining trees, but this was not observed in the boundary data set. We suggest that thedifferences between the models may reflect different scales of habitat selection. Boundaryoccupancy reflects broad distributions of habitat suitability; territory occupancy patternsbetter reveal detailed habitat requirements.6.Regional densities were more closely correlated with the predictions of the boundarybasedmodel than those of the territory-based model, and we discuss the implications ofthis for interpreting habitat association models.7.Synthesis and applications.Provision of winter set-aside fields for summer territoryselection by yellowhammers is an important consideration for farm management whereconservation is a priority. We show that models based on occupancy of individualboundary units (e.g. hedgerows) correlate with the density of territories at the farmscale; thus farm management practices link directly to population sizes through effectson the quality of breeding habitat.

Mark J. Whittingham, Ruth D. Swetnam, Jeremy D. Wilson, Dan E. Chamberlain and Robert P. Freckleton, Journal of Applied Ecology 2005 42 , 270-280