Diet of nestling Linnets Carduelis cannabina on lowland farmland before and after agricultural intensification

摘要

Between the 1960s and 1990s, nestling diet has changed in ways consistent with the impact of agricultural intensification on the availability of seed sources. To compare the diet of nestling Linnets before (1962-64) and after (1996-99) the main period of agricultural intensification in lowland England. Visual estimation of the composition by volume of seeds in the gullets of 279 Linnet broods visited one to three times when nestlings were between four and nine days old during 1996-99. These data are compared with those obtained by repeated visits (approximately 15 per brood) to 62 broods during 1962-64. Several traditional food-plants have been lost or markedly reduced in nestling Linnet diet, probably as a result of declines in weed populations in the agricultural landscape due to intensification of farming practices. In the 1990s, nestling diet was dominated by the seeds of the grassland weed Dandelion Taraxacum officinale and the arable crop Oilseed Rape Brassica napus oleifera. The availability of Oilseed Rape in arable rotations may now be very important to the maintenance of populations of Linnets in intensively managed arable and mixed agricultural systems in the UK.