Functional diversity and habitat specialization of birds as tools to test for forest vegetation disturbance

Forest understory insectivorous birds are one of the most sensitive groups to vegetation disturbance. We evaluated if functional diversity (FD) and habitat specialization (HS) of suboscine species (antbirds-ovenbirds), mainly understory insectivorous birds, could detect vegetation disturbance. Our study areas are two large blocks of seasonal forest in the Atlantic rainforest, southern Brazil: the Iguassu National Park (INP; 187,000ha), which is a well preserved area, and the Biological Reserve of Perobas (BRP; 9,000ha), which had selective logging and fire actions. Because BRP is composed of a mosaic of secondary forest and relatively preserved areas, we tested if the values of FD and HS of this Reserve are lower than INP. We used point counts for four years to census birds in 5 sites of 1km each in both Reserves. Traits used to obtain those FD values were foraging strategies and morphological measurements. Levels of habitat specialization of each bird species was obtained in a previous study. Based on the occurrence of species, we calculated the average of specialization of each bird assemblage of each 1km site in both Reserves. We recorded 24 species in INP and 27 species in RBP. We found that the average HS in RBP was lower than in INP (t = 2.424; df = 7.365; p = 0.044), but found no difference in FD values. However, when considering only the foraging traits, FD (p = 0.048) was higher in INP than in RBP. HS and FD of suboscines were good predictors of vegetation disturbance.