Fruit and flower availability affect bird assemblages across two successional stages in the Atlantic Forest

The Atlantic Forest is highly heterogeneous, with successional stages inducing shifts in food resources for birds. We investigated fruit and flower availability across two different successional stages in a continuous forest and the implications for bird communities. We sampled three sites in primary forest and three in second-growth forest. We established four plots (10 x 10 m) in each site and estimated the availability of zoochorous fruits and ornithophilous flowers and the occurrence of fruit-eating birds and hummingbirds. Unexpectedly, the availability of zoochorous fruits was similar for primary and second-growth stages, but the abundance of ornithophilous plants was higher in primary forest. Specialized frugivores were more abundant in primary forest, whereas abundance and richness of hummingbirds did not differ between the two successional stages. Frugivores responded to fruit availability in both successional stages, while hummingbirds varied according to ornithophilous plants only in the primary forest. Our results stress that the occurrence of bird species can vary according to resources availability in continuous areas, which contributes to high diversity in forests. These findings highlight the importance of preserving large continuous tracts of forests that promote a spatio-temporal distribution of resources, which maintains bird diversity and their interactions with plants.