Has Danish agriculture maintained farmland bird populations?
Rapid agricultural change in western Europe has occurred in the last three decades, at cost to farmland biodiversity, particularly birds. This study reviewed agricultural change in Denmark from 1983 to 2001, to compare patterns of intensification and farmland bird abundance with the UK. Changes in 26 agricultural variables summarized using principal components analysis (PCA) showed consistent changes throughout the period that were similar to the UK. Pig and sheep production, and the extent of winter cereals, rape and fodder maize, all increased. The area used to grow fodder beet and spring barley, the applications of agrochemicals and the numbers of cattle reared all declined. The greatest change in land area in Denmark was the switch from spring- to autumn-sown cereals in the 1980s, almost a decade later than in the UK. PCA described changes in annual indices of bird abundance based on Danish point count surveys from 1983 to 2001, which were most marked during 1983-90, after which ordination values varied little despite continued agricultural change. Of 27 bird species associated with farmland habitat in Denmark, five declined, 10 showed stable trends and 12 increased, compared with 15, eight and four, respectively, among the same species in the UK. Agricultural yields have been sustained or enhanced during the survey period, while most farmland bird species declining in the UK have remained stable or increased in Denmark. Of the five declining Danish species, only lapwing Vanellus vanellus and yellowhammer Emberiza citrinella are associated with predominantly farmland habitat. The timing of the declines suggests that the switch to autumn sowing in Denmark has had little effect on any species. In contrast to the UK, pesticide and inorganic fertilizer use has declined and organic farming has expanded in Denmark since 1983, coinciding with the period of stability/increase in farmland bird abundance. It is not possible to establish any causality from this analysis. The ability of species showing marked declines in Europe to maintain their number and distribution in the Danish landscape in the face of agricultural intensification gives some optimism for safeguarding farmland birds and biodiversity in the future. However, we need to understand the reasons behind contrasting population trends in Denmark and the UK. Synthesis and applications. Marked differences between national patterns of agriculture and the contrasting nature of historical intensification offer the opportunity to contrast the effects of major changes in land-use practice on European farmland biodiversity. Appropriate comparative and individual studies of the effects of changes in specific agricultural management at greater spatial (i.e. supranational) scales are necessary in order to underpin the successful development of future European agricultural policies that will sustain and enhance agricultural yields whilst maintaining farmland biodiversity.