SHRIKES LOVE THE ROADS IN AGRICULTURAL LANDSCAPES? Use of hierarchical partitioning to study the importance of proximity to the roads on the probability that Red-backed Shrike occupy suitable shrubs during breeding: preliminary results in farmlands of Central Italy

Roads are a pervasive feature on the landscape and their ecological effects on vertebrate wildlife have been well documented. Indeed, the main types of effects described have mainly negative consequences on birds and other vertebrates. The major effects of roads on birds include habitat fragmentation, traffic noise and direct mortality from road kills. However, others passerines like the Red-backed Shrike, Lanius collurio, seem use the areas close to roads often for nesting and hunting purposes. The aim of this work was to study the importance of road proximity in the selection of suitable shrubs for nesting by the Red-backed Shrike in the farmlands of Central Italy. The study was conducted in a breeding territory of the species in the River Foglia catchment area in Central Italy. The bird data were collected during the 2009 breeding season using a complete mapping, in an area of 600 ha. Each shrub was digitized and classified as “suitable” according to previous studies on the ecology of the species in the same region: vegetal species, size and density of foliage. The suitable shrubs were classified as “occupied” or “unoccupied” by a nest. Were also calculated the following environmental parameters: altitude, nearest road distance, shrub shape, shrub surface, shrubs density in a fixed radius of 50 m, nearest shrub distance, landscape fragmentation and land-use coverage. The relationships between nesting and environmental parameters were examined using a GLM stepwise backward procedure to select the most significant variables using the AIC criterion. In order to quantifying the effects of every independent variable (in particular “nearest road distance”) was used the hierarchical partitioning protocol, that employs goodness of fit for each possible models, with R program. 739 suitable shrubs were mapped, with a density of 0.62 shrubs/ha. All of the 42 nests studied were located in shrubs, with a density of 0.35 pairs/10 ha. The mean distance of occupied shrubs from the nearest road was 12.5 m. In 76 % of the cases the nests were positioned less than 25 meters from roads. The analysis of the relative importance of every variable for the models showed that the road distance is one of the most important variables in relation to the probability of Red-backed Shrike nesting in the suitable shrubs. The preliminary results suggest that in homogeneous agricultural landscapes, Red-backed Shrike seems to build the nest mainly on the suitable shrubs nearest to the roads, preferring these also if there are other available shrubs with similar characteristics which are located away from roads. It is reasonable to argue that suitable shrub for nesting and the contemporary presence of bare soil or open spaces for hunting, both of which exist close to countryside roads, might represent the favorable components of the breeding habitat selections of Red-backed Shrikes. Our results could provide useful indications for the census techniques and conservation of the species; however, more accurate researches are needed to better explain their irregular distribution in agricultural landscapes.