Shift in crop preference during the breeding season by Yellow Wagtails Motacilla flava flava on arable farms in The Netherlands

Abstract

Dutch farmland bird populations are in steep decline as a result of agricultural intensification. The Yellow Wagtail (Motacilla flava flava) is one of those species, but its decrease has mainly occurred in grasslands, with its population in arable areas remaining more or less stable. In contrast, populations of other typical birds of arable habitats, such as the Skylark (Alauda arvensis) and Grey Partridge (Perdix perdix), are declining strongly in this habitat type. The favorable status of the Yellow Wagtail is probably caused by the crop-mosaic composition of arable farms in The Netherlands, which often includes winter cereals, potatoes, and sugar beet. This study focused on crop preference by the Yellow Wagtail during the breeding season. Early in the breeding season Yellow Wagtails showed a strong preference for winter cereals. However, as the breeding season progressed, their preference gradually shifted to broad-leaved crops, especially potatoes. Measurements of the crop structure as an indication for vegetation height or bare ground, revealed that the Yellow Wagtail strongly preferred crops 20–40 cm high. Higher crops were also used more than expected based on a uniform distribution, but to a lesser extent, and crops <20 cm in heigth were not preferred at all. In terms of ground coverage, Yellow Wagtails preferred crops providing a ground coverage of at least 60%. There was a negative association between Yellow Wagtail numbers and crops providing <20% ground coverage.