[T]he Amazon rainforest contains more than 1,500 bird species. Around a quarter of them are found nowhere else on Earth. Many of these birds have evolved to fill a specific role – whether that means eating particular types of insects, or scattering a certain size of seed….A new paper published in Proceedings of the Royal Society explores the link between deforestation in the Amazon and local bird diversity…[B]ird data was collected in 330 different sites in the Brazilian state of Pará, including arable and pastoral farmland and both primary and secondary forests. Primary forests are the original native vegetation, now increasingly degraded by logging and wild fires. Secondary forests are those which grow back in areas, often farmland, which have been abandoned by people…
The study focused on seed dispersal and insect predation, two ecosystem processes where birds play important roles. Fruit-eating (or frugivorous) birds spread the seeds of forest trees. Insect-eating (insectivorous) birds ensure that any germinating saplings have a fighting chance at survival. ..[S]witching from primary tropical forests to farmland dramatically reduced the “services” birds were able to provide.
This may seem fairly intuitive so far, given that there is a world of difference between a forest and cattle pasture. However, more significantly it was found that the traits were only partially restored in regenerating secondary forests. These areas have been branded as the “forests of the future” but we found them coming up short. These “forests of the future” cannot conserve all the biological interactions realised in primary forests, undisturbed or otherwise, which are essential for biodiversity conservation. Once large seed-dispersing birds such as guans or cotingas are lost in an area, trees species with large seeds find it harder to recover. Regeneration becomes unlikely or impossible. Research from Brazil’s coastal Atlantic Forest has shown that the loss of such key species is driving the evolution of palm trees with smaller seeds. Some of these links may have been lost before we even knew them….The sorts of generalist insect-eaters that come to dominate farmland aren’t generally able to capture the well-disguised insects found in adjacent patches of forest.
Excerpt from Without birds, tropical forests won’t bounce back from deforestation, the conversation.com, Nov. 8, 2016