Assessment of the vegetation structure influence on bird communities’ occurrence in Iberian agro-forestry systems.

The main objective of this study is to identify the vegetation/habitat measures having a greater influence on the presence of avian species in two types of agrossystems located in the South of Portugal. This approach for classifying habitat types allows a consistent development of wildlife management strategies. Four line transects were defined. Two were located near Évora (Santa Sofia and Valverde) and the other two in Apostiça (Lagoa do Golfo and Marco do Grilo). Several variables were measured to describe the vegetation as a habitat. The linear transect technique was used in the bird sampling. Multivariate statistics were used to analyse the relation between the presence/absence of avian communities and the different vegetation cover measures. These include vegetation vertical structure, percentage of vegetation cover types, and vegetation diversity measures. The relation between avian diversity and vegetation structure descriptors, as well as the vegetation diversity, was analysed using simple regression methods. Physiognomic gradients were identified based on structural variables. The bird communities seem to respond to the above mentioned structural differences. Moreover, the diversity of these communities is related to the percent cover of shrub and tree layers