JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. Ecological Society of America is collaborating with JSTOR to digitize, preserve and extend access to Ecology. Abstract. We sampled understory insectivorous birds in Amazonian forest fragments from before isolation through 9 yr after isolation. We accumulated 3658 mist net captures of 84 insectivorous species in five 1-ha fragments and four 10-ha fragments. Abundance and species richness declined dramatically after isolation, even though fragments were separated from continuous forest by only 70-650 m. Three species of obligate army ant followers disappeared within the first 2 yr after isolation. Mixed-species flocks containing 13 commonly netted species disintegrated within 2-3 yr after isolation, although three species that dropped out of flocks persisted in fragments. Among insectivores not associated with flocks or army ants, only two species of edge specialists were unaffected by fragmentation. Overall, loss of forest insectivores was not compensated for by an increase in nonforest or previously uncommon species.Secondary vegetation surrounding fragments strongly affected use of fragments after isolation. Fragments surrounded by Vismia, the dominant regrowth where felled forest was burned and temporarily used as cattle pasture, remained depauperate. In contrast, many species returned to fragments by moving through regenerating forest dominated by Cecropia, which occurred in areas where the felled forest was not burned. Both 1and 10-ha fragments surrounded by Cecropia were used by ant followers by 5 yr after isolation. Mixed-species flocks reassembled in 10-ha fragments surrounded by Cecropia by 7-9 yr after isolation, and augmented their group territories by foraging in secondary forest outside fragments. Solitary species were more variable in their responses, although several species returned to 10-ha fragments surrounded by Cecropia. Terrestrial insectivores, such as Sclerurus leafscrapers and various antbirds, did not return to any fragments, and appear to be the group most vulnerable to fragmentation.Ordination of the insectivore community showed that 1-ha fragments diverged from their pre-isolation communities more than did 10-ha fragments. Communities in 10-ha fragments surrounded by Cecropia were more closely associated with pre-isolation communities than those in fragments surrounded by Vismia. Over time, communities in 10-ha fragments surrounded by Cecropia became more like pre-isolation communities, although communities in other fragments generally continued to diverge.

We examined the distributions of nine species of terrestrial insectivorous birds in 4‐ to 14‐year‐old rainforest fragments north of Manaus, Brazil. We surveyed 11 fragments of 1, 10, and 100 ha, 95 ha of secondary vegetation, and nine continuous forest plots (controls) of 1–100 ha. We augmented standard spot‐mapping with extensive playback surveys. The fragments had been sampled with mist nets before isolation, so our results could be compared with the pre‐isolation distribution. For the nine species, there were 55 cases of local extinction in the 11 fragments between about 1 year after isolation and the time of our surveys. This corresponds to 74% extinction of the local populations in fragments. These extinctions occurred despite the second‐growth connection of some fragments to continuous forest as little as 70 m away. Three apparent colonization events by species not detected before isolation also occurred, but these may also reflect inadequate sampling before isolation. Our comparison of fragments and similar‐sized control plots in continuous forest showed an area effect on species richness in both fragments and control plots, but fragments had fewer species than control plots of equal size. In a fragmented Amazonian landscape, the full suite of terrestrial insectivores would persist in the short term only in large fragments ( >100 ha), although much larger areas are probably necessary for the long‐term persistence of their populations.

How are rainforest birds faring in the Anthropocene? We use bird captures spanning > 35 years from 55 sites within a vast area of intact Amazonian rainforest to reveal reduced abundance of terrestrial and near‐ground insectivores in the absence of deforestation, edge effects or other direct anthropogenic landscape change. Because undisturbed forest includes far fewer terrestrial and near‐ground insectivores than it did historically, today’s fragments and second growth are more impoverished than shown by comparisons with modern ‘control’ sites. Any goals for bird community recovery in Amazonian second growth should recognise that a modern bird community will inevitably differ from a baseline from > 35 years ago. Abundance patterns driven by landscape change may be the most conspicuous manifestation of human activity, but biodiversity declines in undisturbed forest represent hidden losses, possibly driven by climate change, that may be pervasive in intact Amazonian forests and other systems considered to be undisturbed.