Bird species in rainforest fragments in Brazil that were isolated by deforestation disappeared then reappeared over a quarter-century, according to research results published today in the journal PLoS (Public Library of Science) ONE. Scientists thought many of the birds had gone extinct.

   Lead author Philip Stouffer, an ornithologist at Louisiana State University and co-authors of the paper measured bird populations over 25 years in 11 forest fragments ranging from 2.5 acres to 250 acres in the Amazon rainforest near Manaus, Brazil.

In the first decade of the long-term study, birds abandoned forest fragments and, ornithologists believed, went extinct. Then in the past 20 years, many bird species returned, while others went extinct or remained extinct.

"Through long-term observations of fragmentation in tropical forests, this study provides verification that local extinction is accompanied by continual recolonization, dependent on habitat size," said Saran Twombly, program director in NSF's Division of Environmental Biology, which funded the research.

Bird populations were measured before the deforestation process began, then again in 1985, 1992, 2000 and 2007. Both extinction and colonization occurred in every interval. In the last two samples–taken in 2000 and 2007–extinction and colonization were approximately balanced. 

The extinction process started with birds leaving or dying out. Now, they're coming back.

Of the 101 species netted–trapped with a fine-mesh mist net–before deforestation, the researchers detected 97 in at least one forest fragment in 2007.

"A handful of species have "gone extinct," but many more species are in flux," Stouffer said. "They come and go."

The project measured only understory, resident birds and not those that live in the forest canopy or may migrate.

"Our samples are snapshots in time," said Stouffer. "They show that forest fragments have the potential to recover their biodiversity if they're in a landscape that can rebound.

"They're not doomed."

The research demonstrates some of the ways birds exist in a human-modified environment, as well as the effects of allowing a forest to regenerate.

Species biodiversity in today's forest fragments reflects local turnover, not long-term attrition of species, the scientists found.

They think similar processes could be operating in other fragmented ecosystems, expecially ones that show unexpectedly low extinction rates.

source: http://smithsonianscience.org/2011/06/extinct-birds-reappear-in-rainforest-fragments-in-brazil/