Do field margins enrich the diet of the Eurasian Skylark Alauda arvensis on intensive farmland?

To help restore food availability for birds, arable field margins (extensively managed strips of land sown with grasses and forbs) have been established on European farmland. In this study we describe the effect of field margins on the diet of Eurasian Skylark nestlings and adults living on intensively managed Dutch farmland. We tested the hypotheses that field margins offer a higher diversity of invertebrate prey than intensively managed crops, and that the diet of nestlings receiving food from field margins will therefore be more diverse than that of other nestlings. Field margins had a greater variety of invertebrate prey groups to offer than the intensively managed crops. Coleoptera were the most frequently and most abundantly eaten prey group by both adults and nestlings. Together, Coleoptera, Diptera, Lepidoptera, Hymenoptera and Araneae accounted for 91% of the nestling diet. Nestlings ate larger prey items and a larger proportion of larvae than adults. Almost 75% of both adults and nestlings consumed plant material, perhaps indicating a scarcity of invertebrate resources. When provided with food from field margins, the mean number of invertebrate orders in the nestling diet increased significantly from 4.7 to 5.5 and the number of families from 4.2 to 5.8 per sample. Thus, birds that used field margins for foraging could indeed provide their young with more invertebrate prey groups than birds only foraging in crops and grassland.