Widespread, generalist birds are riding the wave of Amazon deforestation

Blog written by Cameron L. Rutt, PhD Candidate at Louisiana State University, USA. Read the full paper here

Experimental clearcutting (north of Manaus, Brazil) leaves behind habitat that is very unlike the surrounding rainforest. Photo by Angélica Hernández Palma. 

Recent forest fires throughout the Brazilian Amazon’s southern tier have reignited the international consciousness, bringing renewed focus to the wake left behind by the blazes—deforestation. But, this is not a new phenomenon in the world’s largest rainforest, especially along the so-called “arc of deforestation,” in the Brazilian Amazon’s southern and southeastern reaches. Over the past 30 years, deforestation practices across this entire region have carved a California-sized hole in this once seamless forest, adding to the now 20% that has been clearcut.

One idea is that species might colonize recently cleared areas by traveling along roads, which offer corridors of habitat for species that cannot use mature forest. This is BR-174, the major highway that slices through the rainforest for 1000 km north of Manaus. Photo by Cameron L. Rutt.

Large clearings for agriculture and cattle ranches stand in stark contrast to the surrounding forested areas, which teem with rich plant and animal communities. We now have decades of research following deforestation that illustrate in sobering detail just how devastating habitat loss is for the unique forest biodiversity. But we also need to learn about the kinds of species that colonize and tolerate these human-modified landscapes. What is the legacy of these newly cultivated habitats?

Yellow-headed Caracara (Milvago chimachima) is part of the vanguard of species that arrived after the creation of three cattle pastures. Photo by Cameron L. Rutt.

The first question this begs is one of duration—does it take decades for animals to find and colonize these new areas of disturbance? A large-scale experiment in the central Amazon that once housed three cattle ranches helps us to answer that question for birds. Now largely abandoned by ranchers, scientists have been cataloging birds at the Biological Dynamics of Forest Fragments Project, for nearly 40 years.

The Variable Chachalaca (Ortalis motmot)—a species that favors dense vegetation following disturbance—has now made inroads into expansive tracts of rainforest. Photo by Anselmo d’Affonseca

We used these uniquely rich bird inventories to ask a series of simple questions. When an area is clearcut, do adjacent forest birds move in? If not, what habitat supplies the new arrivals? How quickly do they find these cracks in the Amazon? And how long do these novel avian communities linger? We found that there are dozens of outside species such as flycatchers and tanagers that almost immediately filled these anthropogenic cracks in the forest, even in the absence of large-scale transformation of the landscape.

The Shiny Cowbird (Molothrus bonariensis) is one of about three-dozen widespread habitat generalists that quickly colonized the cattle ranches after clearing. Photo by Cameron L. Rutt.

In all, more than 100 bird species appeared that are not typically found in the surrounding pristine rainforest, and about three dozen of these established small populations within the disturbances. Moreover, these birds arrived quickly—the vast majority appeared within the first decade after the ranches’ establishment. Finally, a disproportionate number of these birds are widespread generalists, species that are commonly found in close association with humans. This includes birds regularly encountered in the largest Amazonian city of Manaus and species that frequent regional backyards and gardens.

A number of established colonists, such as this striking Chestnut-bellied Seedeater (Sporophila castaneiventris), have declined as the forest recovers. Photo by Anselmo d’Affonseca.

This study also serves as an important benchmark to describe what happens when the landscape begins to heal. We found that as the forest recovers on the abandoned cattle ranches, these widespread birds began to retreat and disappear from the landscape because they were restricted to the disturbances. This is good news for the many specialized forest birds that can now regain lost habitat, but which could not survive in pastures or clearcuts. Therefore, for the health of the Amazon rainforest, we should minimize the intensity of human land-use and, should deforestation occur, allow the forest to reassert itself as soon as possible.

However, birds like this female Black-throated Antshrike (Frederickena viridis) rely exclusively on intact, pristine rainforest and do not occur in regenerating forests, even after >30 years. Photo by Cameron L. Rutt

Deforestation rates in the Amazon are once again on the rise, further degrading the habitat of hundreds of species of birds. It is therefore critical that conservationists understand how these organisms, as well as the novel communities of widespread generalists, are coping with these large-scale landscape changes. Only then will we be able to develop best management practices for these impoverished habitats. Although this summer’s headline-grabbing fires in Brazil have ratcheted up the pressure for policymakers to stem the tide of Amazonian deforestation, we shouldn’t wait for another severe burning season to flame our interest and outrage about the state of the world’s most diverse forest.   

This work would not be possible without support from the Biological Dynamics of Forest Fragments Project and funding by the US National Science Foundation (LTREB 0545491 and 1257340).

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