Flitting from tree to tree in the lowlands of the Amazon rainforest is a little emerald bird called the yellow-billed jacamar. The jamacar is just one of the hundreds of species that depend on the Amazon to survive, and that are adversely affected by clear-cutting. But there’s hope for some of these birds according to a study in The Auk.
More than half of Amazonia is protected, but many countries continue to clear the rainforest. In Peru, recent analysis of satellite and field surveys suggest that gold mines in the Amazon have expanded 400 percent in less than 15 years. The mines, many of which are small-scale or illegal, not only clear trees but also leave a trail of toxic waste that damages surrounding lands and waterways. Forest is also removed for timber and agriculture. In Brazil alone, an area of forest larger than Poland has been knocked down in the past two decades. Typically these lands are used for cattle grazing and abandoned within five years. The result is a patchwork quilt of old forest and disturbed lands.
Many birds are trapped within the islands of forest that remain. “When there are hard borders, like pastures or young secondary growth or roads, they are often literally imprisoned,” Louisiana State University biologist Luke Powell, first author on the study, told Mongabay.com.
Fortunately, after the lands are abandoned, the rainforest can reclaim them and the growth of secondary forest offers the birds’ a means of escape. From 1992 to 2011, Powell with colleagues at Louisiana State and Brazil’s Instito Nacional de Pesquisas da Amazônia tracked birds in fragmented rainforests as part of the Smithsonian Tropical Research Institute’s Biological Dynamics of Forest Fragments Project. In mist nets they captured 3,735 local flyers traveling on the borderlands between older primary and new-growth.
Using this data, the researchers wanted to determine how long it would take for the population of various species to reach the same levels as before the clear-cutting. To do this, they tracked the presence of birds, grouped by their ecological niche (such as diet or forest-layer habitat) to study the changes over time. The researchers fed this data into a mathematical model to project what the presence of each species would be in secondary forests in the years to come.
On average, bird species require 26 years to recover. Yet there’s significant variation. Frugivorous species, for example, might only need a decade, whereas it could take terrestrial insectivores up to 60 years. The researchers note that particularly in burned lands, the scorched earth takes longer to recover and restore its former bird populations. The findings in Brazil and Peru are a reminder that although the Amazon’s diversity may make it both rich and resilient, our activities there can cast long shadows.