Arthropod-eating birds comprise a diverse group with varying degrees of sensitivity to environmental changes and distinct responses to habitat degradation. In our study, we investigated the impact of landscape and habitat characteristics on the functional diversity of insectivorous birds in the Brazilian Atlantic Forest. Our hypotheses are focused on (I) how species composition and functional diversity respond to habitat turnover and nestedness and (II) whether an increase in native forest cover positively influences bird species richness and functional diversity. Our research encompasses 22 different landscapes within the Cantareira-Mantiqueira region, southeastern Brazil, including native forests, pastures, and marshes, within 1 km radius buffers. To assess functional diversity, we employed beta pair and beta multi-function indices for each environment type. Generalized mixed linear models were calculated to examine the effects of the native forest cover gradient and environment type on functional diversity. Our findings indicated negative effects of increased native forest cover on functional diversity indices. Bird communities were susceptibility to turnover in pasturelands, to nestedness in marshes, and both species nestedness and turnover in native forests. These results may be partially due to the predominantly second-growth, small-sized, and early successional stages of the native forest fragments in the region. These findings underscore the intricate interplay between landscape characteristics, habitat types, and bird functional diversity within the Brazilian Atlantic Forest. They also highlight the significance of considering habitat quality and succession stages in conservation efforts in this region.

Arthropod-eating birds are a heterogeneous group, with different levels of environmental sensitivity and diverse responses to habitat degradation. In this paper, we tested the effects of landscape on the functional diversity of insectivorous birds within the Brazilian Atlantic Forest. We predict that (I) species composition and functional diversity are shaped by turnover and nestedness across different habitats, and (II) the gradient of forest cover has a positive effect on bird species composition and functional diversity. We used data from 22 landscapes of the Atlantic Forest in the Cantareira-Mantiqueira region (Brazil), within buffers of 1 km radius, surrogating three types of environments (i.e., forests, pastures, and swamps). The components of β-functional diversity were calculated using the beta pair and beta multi-function for each type of environment, and the effects of the forest cover gradient and environment type were tested using linear models and GLMM, respectively. Our results showed that the forest cover gradient and the type of environment had a negative effect on the indices of functional diversity, contrary to our expectations. Pasturelands and marshes were susceptible to turnover and nestedness, respectively. The beta diversity of forests was influenced by both species nestedness and turnover. The regional native forest fragments are generally small-sized, and in early successional stages, which could explain the patterns we found. The presence of secondary forests may have affected the expected pattern of functional diversity, therefore, caution is needed when interpreting this, since the way in which compensatory dynamics may not involve real functional compensation.