EFFECTS OF FOREST FRAGMENTATION ON UNDERSTORY HUMMINGBIRDS IN AMAZONIAN BRAZIL

We sampled understory hummingbirds in Amazonian forest fragments from before isolation through nine yeats after isolation We recorded 377 ca ptures of eight species in five I-ha fragments and four 10-ha fragment s. The three species netted before isolation Phaethornis superciliosus , Phaethornis bourcieri, and Thalurania furcata, were nearly equally a bundant at that time. After isolation abundance of P. bourcieri and T. furcata did not change, but P. superciliosus became nearly twice as c ommon. Five additional species that were netted only after isolation r epresented about 10% of the post-isolation sample. The species recorde d only after isolation were forest species usually found above the lev els of nets;fragments were not colonized by nonforest species. Use of fragments did not differ between 1- and 10-ha fragments. The landscape surrounding the fragments included active cattle pasture, abandoned p asture, and Cecropia-dominated second growth, but this variation had l ittle effect on use of fragments by hummingbirds. The results suggest that these understory hummingbirds can persist in a matric of fragment s, secondary growth, and large forest patches. This response is much d ifferent than that of the insectivorous birds that dominate the unders tory bird community at the site, which are much more vulnerable to fra gmentation.