Spring and summer habitat preferences of little bustard in an agro-pastoral area in Sardinia (Italy)

摘要

The little bustard Tetrax tetrax (Aves, Gruiformes) is a threatened bird species, which is highly reliant on extensively grazed semi-natural grasslands. It is one of the more rapidly declining species in Europe due to the widespread intensification ofagricultural practices and consequent abandonment of agro-pastoral activities. Therefore, understanding its habitat requirements in different seasons is crucial to implement adequate habitat management measures. Previous knowledge of habitat preferenceof the little bustard in Sardinia, which nowadays supports the only remnant isolated population present in Italy, is only available for the breeding season. We conducted surveys of displaying males in spring and of mixed flocks (of different age and sexclasses) in summer and quantified habitat requirements in the two seasons using logistic regression analysis. Overall, we detected 85 displaying males in spring and seven mixed flocks (totalling 77 individuals) in summer within the study area. Interestingly, habitat preference models evidenced contrasting needs between the two different seasons: Males occurrence in spring was higher with greater fallow cover and further from water, whereas in summer flock occurrence was negatively related to fallow cover. This seasonal change in fallow preference is likely due to the effect of grazing livestock on this land-use. Extensive grazing is known to shape adequate habitat structure for displaying males in spring. On the other hand, grazing animals in summer may deplete the already limited food resources (i.e. green plants) available during this dry period of the year and when energy requirement for the little bustard is high due to feather moulting. This may explain the observed avoidance of fallow cover in summer. Conservation efforts in Sardinia should aim at maintaining a mosaic of diverse habitats that may provide complementary resources at any given time of the year that would benefit this and other grassland species of conservation concern.