Beginning in 1979, rainforest cutting produced a series of forest fragments near Manaus, in the Brazilian Amazon. Research in the fragments, which began while they were still connected to forest, has produced important insights into the consequences of rainforest loss in the tropics. Many bird species went extinct in fragments, resulting in much different communities in fragments compared to undisturbed forest. As expected, effects were most pronounced in the smallest fragments, 1-10 ha, but species were also lost from the larger 100 ha fragments. It was also found that the bird communities in the fragments changed over time in response to the regrowth or clearing of vegetation in the deforested areas surrounding them. Most results so far have come from a standardized program of sampling by catching (then releasing) birds near ground level. Over the next five years, this sampling will be continued, but additional techniques will be added to describe the entire bird community in fragments and control sites. How birds use forest regrowth surrounding fragments will also be examined. This research will contribute to an understanding of how 30 years of landscape change affects the world's most diverse bird community, and will provide information on how management of regrowth and forest patches can benefit birds.
We work with birds in a series of rainforest fragments in the central part of the Brazilian Amazon, north of the city of Manaus. Our overarching question is what happens to rainforest birds as Amazonian rainforest is lost. The fragments where we work, called the Biological Dynamics of Forest Fragments Project (BDFFP), were cut out of the forest in the late 1970s and early 1980s as agricultural development expanded into the central Amazon. A unique advantage of our project is that the fragments were first surveyed before they were isolated from continuous forest, giving us over 30 years of continuous monitoring. In the first few years after isolation, abundance of birds declined dramatically in the fragments, and many species went locally extinct in individual fragments. These losses were most dramatic in small fragments (about the size of two football fields) but also occurred in our largest fragments, which are 100 times bigger. With the passage of time, the landscape setting has become a crucial part of the story for birds in the fragments. Thankfully, most of the rainforest within 100s of km of our sites remains intact. The ranches that were established now have minimal agricultural activity, and large areas support young regrowth forest. Through our monitoring over the last five years, we now know that many species of birds return to the fragments through this regrowth forest (the regrowth is often called ‘secondary forest’ or ‘second growth’ to distinguish it from the old-growth or ‘primary’ forest that it replaces) . Birds continue to become locally extinct in fragments, but this loss is balanced by recolonization by other species. An important technique for our work is capturing and releasing birds using fine nets (called ‘mist nets’ by ornithologists). This gives us a close look at birds in the hand, from which we can use subtle plumage patterns to determine a bird’s age. This information, combined with recapture of birds that we can identify individually thanks to numbered leg bands, tells us that many of the recolonists of fragments are young birds that may just be passing through. On the other hand, we also know that a subset of species persist and breed in fragments. We’ve focused a great deal of our work on the interface between fragments and second growth. By putting radios on birds living near the edge, we know that some species will readily use the areas outside fragments, even though they concentrate their activity in the taller forest inside the fragments. Direct observation of movements by mixed-species flocks of birds tell a similar story; even though the birds sometimes venture outside the fragments, their foraging is concentrated, and appears to be most successful, inside the fragments. Collectively, these observations suggest that the second growth is becoming increasingly valuable for forest birds, but that it has not yet reached the point of being equivalent to primary forest. Projections from our long term data suggest that about 50 years will be necessary for normal movements of the full suite of species we’ve monitored since the 1970s. Another emphasis of our work has been to document the bird community, or full set of species, in undisturbed forest. As expected, old-growth forest supports an incredibly diverse set of bird species. We found 228 species on a 1 km2 plot. Many of the species occur at quite low densities, and the low density species are not just eagles or macaws; species comparable to mockingbirds or chickadees familiar to North Americans require territories the size of 5-10 football fields. Moreover, any given plot, even one as large as 1km2, misses a significant number of forest species present in the general area. Collectively, these results suggest that extremely large areas of intact forest will be required to support the full complement of central Amazonian species at densities high enough to maintain populations. All of our research is done with collaborators from Brazil’s National Institute for Amazon Research (INPA), allowing us to help train Brazilian ornithologists, particularly graduate students. Through our long-term work, we have been able to prepare materials that make the avifauna of the BDFFP one of the best known in all of Amazonia. Our two most important contributions are a set of CDs that include vocalizations for almost all of the species at our sites, and a visual guide to the age classification of birds. We hope these resources and our capacity building will improve the foundation for ecological studies of birds in this fascinating, but threatened, part of the world.
