Changes in agricultural land-use and breeding performance of some granivorous farmland passerines in Britain

Abstract

Analysis of the variation in demographic rates with respect to environmental heterogeneity in space and time represents a valuable technique with which the causes and mechanisms behind population changes can be elucidated. Here, extensive spatially referenced data on agricultural land-use at the 10 km square scale for England, Wales and Scotland were analysed in relation to similar data on breeding performance for six granivorous passerines which have declined in recent years. Five principal component axes described the variation in agricultural land-use from 1969–1988 adequately and explained the variation in breeding performance (measured as daily nest failure rates, chick:egg ratio, clutch size and brood size) to varying degrees across species. The overall influence of agricultural land-use tended to be species-specific, with principal component axes describing gradients between pastoral and arable agriculture and between intensively arable and more extensive agriculture being particularly important, but having different effects across species. The clearest general pattern suggested that more intensive agriculture tends to be associated with poorer breeding performance. Although influences of agricultural land-use on breeding performance are unlikely to have driven the major, long-term declines of any of the species except linnet, the results are consistent with those of other work suggesting that less intensive farming provides better habitat for farmland birds. The results both suggest directions for the management of farmland which could aid population recoveries via improvements in breeding performance and provide hypotheses for further intensive field studies of the influences of farming practices on bird populations.