Abbondanza delle cavità arboree e occupazione da parte della civetta nana nelle foreste Parco Naturale del Mont Avic

Understanding the role of natural components of forests, such as tree cavities, is an important step to determine an appropriate sustainable managing strategy in a conservation biology context. Tree cavities have been defined as “keystone vegetation structures”, a feature which increases biodiversity by having a crucial role in providing ecological services for other species. More specifically, tree cavities provides an essential habitat for nesting, roosting, foraging and hibernating for a wide group of animals, including small mammals like bats and rodents, forest passerines and owls, insects and reptiles. Providing more information on natural cavity abundance and availability is needed for a better understanding of the ecology and distribution of populations of secondary cavity nesters, e.g. the Eurasian Pygmy Owl. This thesis aims to estimate the abundance and quality of excavated tree cavities in the alpine forests of the Mont Avic Natural Park area and to test a correlation with environmental drivers such as altitude, topography, vegetation type, wood hardness and solar radiation. The results might provide evidence on what more likely affect woodpeckers preference, resulting in finding the habitat characteristics more suitable for excavated tree cavities formation. We used a Generalized Linear Mixed Model (GLMM) approach to predict the occurrence probability of the tree cavities, based on biotic and abiotic factors. We therefore used playback presence data to produce a Generalized Linear Model (GLM) to discuss the significance of tree cavity abundance for pygmy owls and whether their availability is limiting the population, basing on evidence of chosen habitats for territory. The results bring new information on population distribution and habitat preference of both the studied species Glaucidium passerinum and Dendrocopos major and provide clues for forests managing practices that favors tree cavity users species. To our knowledge this is the first attempt to quantify tree cavities abundance in the Italian alps and assessing their significance for second cavity nesters, aiming to bring new information for conservation biology purpose and forests management.