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Birds wanted: Recovering forests need avian assist 

  • Clearing swaths of rainforests can permanently drive away or kill off birds that are important partners in the regeneration of the forest, the study finds.
  • The study surveyed 330 sites in the Brazilian Amazon, turning up 472 species of birds.
  • The analyses demonstrate that recovering forests don’t have the diversity of birds needed to ensure their survival.
  • The authors say that their findings point to a need to preserve standing forests, even if they’re heavily degraded.

The disappearance of birds may hamper tropical forests as they struggle to recover from the shock of intensive logging, agriculture and ranching, a team of ecologists reports.

Birds play a vital role in the health of the forest. They’re important conduits for tree reproduction, shuttling seeds throughout the landscape. And they rein in hungry plant-eating insects. Even when we humans remove some trees through selective logging or burning, a lot of birds stick around and help maintain the health of the forest, the researchers found.

But clearing swaths of rainforests can permanently drive away or kill off birds that are important partners in the regeneration of the forest, write the authors of a paper that appeared in the journal Proceedings of the Royal Society B in December.

A green-tailed jacamar (Galbula galbula), an insectivorous bird found in the Amazon and pictured here in Colombia. Photo by Rhett A. Butler

“The trees of a forest may look healthy, but if the animal species required for pollination or seed dispersal are gone, then looks are deceiving,” said Joseph Tobias, an ecologist at Imperial College London and one of the study’s authors, in a statement. “The trees are also likely to disappear over time.”

To get at the complex relationship between forest health and the animals that live there, the team counted the number of bird species – 472 in total – present in 330 study sites representing a variety of forests, farmland and tree plantations in the Brazilian Amazon. From satellite imagery, the researchers were able to determine the recent history of the landscape they found those species in – whether it was undisturbed primary forest, pasture for cattle or somewhere in between, for example.

Beyond just the species of birds, they also looked at the roles that certain types of birds played in the ecosystem. Taking advantage of specimens in museum collections, the authors looked at what they called “functional traits.”

The fruit-eating chestnut-eared araçari (Pteroglossus castanotis), pictured here in Colombia. Photo by Rhett A. Butler

These traits included the shape of the beak, pointing to what sort of seeds a certain bird might go after and making that type of bird important to a particular tree’s survival. Or, the beak shape might indicate a bird’s inclination for picking off leaf-eating pests, thus allowing young trees to grow.

As Tobias and his colleagues anticipated, the number of bird species was highest in pristine tropical forests, and they found that quite a few birds stuck around in selectively logged forests. Even occasional burning wasn’t too much of a deterrent for many bird species.

But as humans put more pressure on the forest and change its structure, they found fewer birds that spread seeds throughout the forests and that manage ravenous insects. Their analyses of that trend suggest that, even as trees start to grow back, recovering forests still lack critical allies that will help ensure their longevity.

“Our findings are a warning flag that we can’t just look at a snapshot of forest health as it appears now,” Tobias said in the statement. “[W]e need to think about preserving the ecosystem processes that will allow forests to survive in the future.”

And that might bring new value to degraded forests.

“To maintain the capacity of rainforests to regenerate, we need to support land-use management policies that [maximize] the extent of mature forests that have never been fully cleared, even if they are highly disturbed,” he added.

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Banner image of the insectivorous rufous motmot (Baryphthengus martii) in Costa Rica by Rhett A. Butler.

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