A review of the abundance and diversity of invertebrate and plant foods ofgranivorous birds in northern Europe in relation to agricultural change

This study reviews the diet of 26 granivorous bird species of European temp erate farmland, and evidence for the effects of agricultural practices on t heir invertebrate and plant foods, in order to assess whether the latter co uld have contributed to recent widespread population declines of farmland b irds. Cereal grain and seeds of Polygonum (knotgrasses and persicarias), St ellaria (chickweeds) and Chenopodium (goosefoots) are important for the bir d species considered. Seeds and green material of Asteraceae, Fabaceae, and Brassicaceae are also widely used, the seeds of Asteraceae particularly by cardueline finches. Declining bird species are not associated with particu lar plant foods, but reductions in overall diversity and abundance of food plants have taken place in intensively managed arable land. Grassland inten sification has reduced floral diversity, and the quantity and diversity of grass and broad-leaved seed produced, but some plant species of value to gr anivorous birds benefit from high-nitrogen environments and may increase in availability (e.g., Stellaria - chickweeds). During the breeding season, A crididae (grasshoppers), Symphyta (sawflies), Araneae (spiders), Chrysomeli dae (leaf-beetles), Curculionidae (weevils), Lepidoptera (butterflies and m oths and their larvae), Aphididae (aphids) and Tipulidae (crane-flies and t heir larvae) are important foods. The first four are associated with the di et of declining bird species, and all are sensitive to insecticide applicat ions. Herbicide applications, increasing specialisation of farmland, loss o f uncultivated field margin habitats, and ploughing are also associated wit h generally detrimental effects on invertebrate groups in arable habitats. In intensively managed grassland, loss of grasshoppers, ants, spiders and l epidopteran larvae removes an important source of food for younger chicks o f a wide range of species. Some phytophagous taxa and predators, however, m ay be more abundant due to the greater standing biomass of plant material. Overall, intensification and specialisation of arable and grassland systems is likely to have reduced the availability of key invertebrate and seed fo ods for birds. However, there is also evidence that reversal of intensifica tion, especially in arable systems can result in rapid recovery of these re sources. In intensively managed farmland, uncultivated field margins, hedge rows, ditches and road verges are likely to become increasingly important s ources of seed and invertebrate food for birds. (C) 1999 Elsevier Science B .V. All rights reserved.