Relative importance of marginal vegetation (shrubs, hedgerows, isolated trees) surrogate of HNV farmland for bird species distribution in Central Italy

The marginal and unproductive elements of farmland landscapes, such as shrubs, hedgerows, isolated trees and uncultivated patches, represent key habitats for many bird species, as far as nesting, feeding and protection are concerned. Anyway this marginal vegetation has been removed due to the agricultural intensification which occurred in Europe during the last decades. In this study, the environmental variables known as marginal vegetation, which explain the presence and distribution of farmland bird species, were analyzed using Generalized Linear Models and hierarchical partitioning protocol. Our results have quantified the total contribution of marginal vegetation on the presence of farmland bird species and also the relative importance of every type of marginal vegetation. These results confirm how these elements, used also as one indication of high nature values of farmlands (HNV), are fit for studies on farmland birds distribution in Central Italy. Some species were more related to hedgerows, while others were related primarily to shrubs and others also to uncultivated marginal patches. The quantification of relative importance of each marginal vegetation is an useful tool for landscape restoration planning. However, as the relative importance was different for each bird species, the studies on farmland birds occurrence remain key to improve the accuracy of predictive frameworks.