Selection of hedgerows by Swallows Hirundo rustica foraging on farmland: The influence of local habitat and weather

Abstract

Capsule The loss of hedgerows may have reduced the quality of agricultural land for breeding Swallows. Aims To test if foraging Swallows select vegetated field boundaries in preference to field centres, if selection is influenced by weather conditions and local habitat type, and if patterns of selection are explained by differences in food availability between the two habitats. Methods Data were collected from paired vegetated field boundaries and field centres in lowland mixed farmland during good and bad weather conditions. The maximum number of foraging Swallows, total foraging time, food availability and local habitat type (adjacent crop type, presence/absence of boundary trees and boundary height) were recorded. Results Foraging Swallows selected vegetated boundaries in bad weather and there was a non-significant trend towards selection during good weather. Hedgerow use increased significantly when the adjacent field was winter wheat, rather than grazed grass. Hedgerows containing trees were used more during good weather, but the strength of the effect is less than that of crop type. The habitat types selected by foraging Swallows were almost always those where measured food availability was the highest. Conclusion Vegetated field boundaries are an important foraging habitat for Swallows and support higher prey densities than field centres, especially when adjacent fields are arable. The loss of hedgerows from agricultural areas, particularly arable ones, may have reduced the quality of farmland as Swallow foraging habitat. An increase in hedgerows and the number of hedgerow trees may improve the quality of farmland as foraging habitat, especially in arable-dominated areas. The effects of this on breeding success and subsequent population trends should be assessed. © 2003 British Trust for Ornithology.