An Altitudinal Gradient for Breeding Birds in Marche Region (Central Italy)

Abstract

Species distribution is determined by several factors. As of 2013, the study area in central Italy, hosts 145 breeding birds. To explore the relationship between species richness and elevation, the study area was divided into 4 altitudinal zones, 600 m wide and 4 belts were indicated for the potential vegetation gradient, as these belts provide a better biological sense as natural marker of climatic and altitudinal transitions. Plotting the number of species by altitudinal belts revealed that species diversity declines in correspondence with increasing elevation. Thus, the lowest altitudinal belt, hilly, has the highest richness in species, (120 sp.), followed by low mountain (110), mountain (80) and high mountain (14). Instead, analysis according to potential vegetation belts indicates that the highest species richness is found in the second lowest belt: coastal (95 sp.), hilly (128), mountain (93) and high mountain (14). The same distribution is obtained for the exclusive species in each vegetation belt (5, 12, 5, 2 respectively) and for birds in Annex I of Birds Directive (2009/147/CE).

From the point of view of conservation, we have to consider not only breeding birds, but also wintering and migrating birds. In fact the distribution map of birds of european conservation concern (breeding, wintering and migrating) emphasizes the highly important role of the coastal area followed by mountain and main rivers connecting them. It is possible to obtain different outcomes as we apply different methods. Potential vegetation belts seem to describe species distribution better than do altitudinal belts. Moreover, potential vegetation belts have more sense than arbitrary altitudinal belts. From the point of view of conservation, considering only breeding birds may provide misleading data. In a planning process, all bird species should be considered: breeding, migrating and wintering.