The importance of drainage ditches for farmland birds in agricultural landscapes in the Baltic countries: does field type matter?

Abstract

Land drainage exhibits a considerable impact on biodiversity. Drainage ditches-a regionally common landscape element-carry a number of benefits for birds associated with farmland. The aim of this study was to quantify a relative value of ditches for farmland birds depending on the type of surrounding fields. Survey data on farmland bird communities and farmland landscape structure across Estonia, Latvia and Lithuania were used. Count plots were situated within either arable fields or grasslands, or their combination and contained two types of ditches, with grassy margins or with tall vegetation such as bushes and trees. Focal species were selected based on their plausible use of ditches. Species richness and abundance of farmland birds were positively associated with the presence of ditches with tall vegetation, but the plausible role of ditches with only grassy margins remained unclear. For some species, the relationship was more pronounced in arable land than in grassland. Regional agricultural policy should support the retention of ditches, especially those with complex structure, in farmland. This action is crucial in landscapes dominated by crop production, as they face the most intense utilisation.