Abstract
Hedgerows are of vital ecological importance, as they play an essential role in protecting the soil and surface and groundwater, maintaining favourable microclimates for many species, dispersing flora and fauna and providing shelter for many protected species. In the context of the climate crisis, they play a part in carbon storage and are of microclimatic interest to local areas. Although they are sometimes seen as a constraint by the farming community, hedgerows are nevertheless ideal habitats for many protected bird species, making their preservation essential for maintaining biodiversity. In this study, we wanted to empirically assess the extent to which hedgerows are home to protected bird species, depending on the type of hedgerow and landscape in which they are found in the Grand Est region. To meet this objective, 1,219 listening points and 1,840 hedgerows were randomly sampled in the region's ten departements in both 2021 and 2022, and based on a stratification according to the density of hedgerows in the landscape. The position of all the birds detected was recorded. As the study took place during the breeding season for the birds, individuals detected on or within the hedgerows sampled were considered to be using the hedgerow as a nesting or resting habitat. The characteristics of the hedgerows were also inventoried. The landscape composition surrounding the hedgerows was subsequently extracted from national spatial databases. Statistical analyses were carried out to study bird assemblages and characterise hedgerow and landscape types. These analyses showed that the bird assemblages present in the hedgerows were relatively homogeneous, as the study focused only on birds that specifically use hedgerows as a breeding habitat, and therefore have similar ecological requirements. Linear mixed-effects models were used to study the effect of hedgerow and landscape variables on three indices related to protected species: the probability of presence of at least one protected species, the abundance of protected species and their species richness. Single-season site occupancy models were also used to estimate the percentage of hedgerows occupied by at least one protected species, taking into account the fact that species detection is not exhaustive in the field. These models showed that almost all hedgerows were occupied by at least one protected species, with the exception of a few low hedgerows that had been damaged and maintained too intensively in arable landscapes, thus demonstrating the ecological importance of hedgerows for protected birds. The presence of protected species in the hedgerows was more closely linked to the characteristics of the hedgerows than to those of the landscape, indicating that hedgerows are of major ecological importance whatever the landscape context. Protected species abundance and species richness were highest in hedgerows that were high, wide, old and had a good habitat heterogeneity (presence of old trees, cavities, dead wood, etc.). The continuity of the hedgerows was also a factor in the higher abundance and richness of protected bird species. The three indices studied were strongly negatively influenced by hedgerow maintenance measures, with lower values in small, damaged and heavily maintained hedgerows. In addition, richness and abundance were negatively affected by landscape homogeneity. Beyond the question of the use of hedgerows as habitat by protected birds, the results seem to argue in favour of preserving and restoring heterogeneous rural landscapes, as well as preserving riparian forests and hedgerows in the broadest sense. Suggestions were made for improving the hedgerow sampling protocol and reducing the detection bias identified in this study. Prospects for extending the study of hedgerow use by protected species to other taxa are also presented.