The distribution and colony size of barn swallow in relation to agricultural land use

1. The barn swallow Hirundo rustica is a semi-colonial passerine that has declined in some parts of its European range, perhaps as a result of agricultural change. So far, however, swallow breeding populations have been analysed mostly in north-western Europe. We studied their distribution, abundance, foraging habitat and breeding performance on 125 farms in Italy in relation to current and past livestock farming and agricultural practice. 2. Swallows foraged within 400 m of the farms on which they bred and had a preference for feeding over hayfields. In logistic and multiple regression models, cross-validated on independent locations, the presence of cattle or pigs in the period 2–5 years beforehand best predicted swallow presence on a farm and, in combination with the presence of stables with traditional architecture, explained 40% of the variance in colony size. 3. Breeding occurred later on farms with no cattle, and fledging success declined with the number of cattle per farm. 4. This study provides the first evidence from central and southern Europe that livestock farming and the architecture of rural buildings affects the distribution and abundance of barn swallows. The data also show how historical ecological information may play an important role in determining current influences on the distribution and abundance of a breeding bird. 5. By augmenting perspectives on swallows at a European scale, our results have important implications for the management and conservation of their breeding populations and allow inferences about the effect of agriculture on future demographic trends.