Habitat use and diet of skylarks Alauda arvensis wintering on lowland farmland in southern Britain.
Abstract
The habitat use and diet of skylarks (Alauda arvensis) 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, England (UK) were counted monthly to examine habitat use. 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. Sugarbeet stubbles held high densities of birds. Rotational set-aside was occupied more frequently and held higher densities than non-rotational set-aside. 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. 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. Broadleaved 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 broadleaved weeds was positively correlated with their availability. Broadleaved weed seeds did not make up a significant dietary component in any crop. Results showed 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 sugarbeet stubbles through the winter, particularly in large open blocks, will improve conditions for skylarks in winter. Whole-field rotational set-aside, particularly as naturally regenerating cereal stubbles, provides good winter food resources for skylarks.