Breeding bird assemblages in a Mediterranean mature beech forest: evidence of an intra-seasonal stability

Abstract

In this study, we obtained data on the structure of two intra-seasonal breeding bird assemblages of a Mediterranean low-altitude beech forests (about 400 m a.s.l.), an ecosystem type of high eco-biogeographic interest and little known in this sense. We sampled 22 breeding bird species (20 sedentary species and two long migrants) with the point count method. Both mean values of species richness and abundance increased from March–April to May–June periods, but differences were not significant. The Shannon diversity index showed a weak increase between early and late spring. We observed an increase of α, β and γ-diversity values from early to late spring. Diversity dominance curves showed a partial coincidence between the two intra-seasonal periods, with a significant difference in slope. Although our low-altitude beech forest showed a relatively low number of species, we observed higher values of total abundance when compared with other beech forests of Central Italy at higher altitude. As a confirmation, our null model analyses of niche overlap revealed no non-random patterns of the temporal distribution of sightings, thus widely supporting the general hypothesis that the bird assemblages of low-altitude beech forests are indeed stable intra-seasonally. The only observed differences between assemblages in the two intra-seasonal periods are limited to the occurrence of two migrant species in the late-spring assemblage (Oriolus oriolus and Upupa epops) that change the slope of the relative diversity/dominance curve (significant different to the early spring curve). Although previous research highlighted the role of altitude in influencing species richness and abundance, this is the first study to analyze the intra-seasonal structure of bird assemblages inhabiting Mediterranean beech forests at low altitude.