Oct. 26 (UPI) -- After decades of studying Amazonian ecosystems, scientists at Louisiana State University realized they were seeing fewer and fewer birds that forage on and near the forest floor.
"What we think is happening is an erosion of biodiversity, a loss of some of the richness in a place where we would hope biodiversity can be maintained," Philip Stouffer, professor of conservation biology at LSU, said in a news release.
Since 1991, Stouffer has been leading research expeditions into some of the most remote parts of the Amazon rainforest, north of Manaus, Brazil. Around 2008, he and his graduate students started noticing that some of the birds they used to see in abundance were becoming hard to find.
Researchers set out to quantify their observations, collecting detailed observation data from 55 test sites. With the help of computer models, researchers compared their observations to datasets spanning 35 years.
Stouffer and company detailed their analysis in a new paper published Monday in the journal Ecology Letters.
"It's a very robust dataset from a variety of places collected over many years. It's not just some fluke," said study co-author Stephen Midway.
"It looks like there's a real pattern and it looks like it could be linked to things we know are happening with global climate change that are affecting even this pristine place," said Midway, an assistant professor at LSU and an expert in computation biology.
The data showed the decline of floor-foraging birds has been slow but steady -- and could have been easily overlooked.
"Our nostalgia was correct -- certain birds are much less common than they used to be," Stouffer said. "If animal patterns are changing in the absence of landscape change, it signals a sobering warning that simply preserving forests will not maintain rainforest biodiversity."
Researchers found that bird species that have declined the most are those living and foraging near the forest floor, birds that feed on insects and small invertebrates -- species like the wing-banded antbird, or Myrmornis torquata. The new data showed one of the Amazon's most adept singers, the musician wren, or Cyphorinus arada, has suffered steady declines over the last three decades.
The white-plumed antbird, or Pithys albifrons, is one of the few floor foragers that remains easy to find. Scientists suspect its ingenious foraging technique has aided the species' resiliency.
The white-plumed antbird follows colonies of marauding ants as they scare up other insects from soil, and it can adapt to different parts of the forest and eat a variety of insects.
Scientists also observed increases in the number of frugivores, or birds that eat fruit and insects, which suggests species with more diverse diets are better able to adapt to ecological shifts.
Stouffer plans to continue investigating the hidden signs of biodiversity loss in seemingly pristine portions of the Amazon.
"The idea that things are changing, even in the most pristine parts of our planet yet we don't even know it, illustrates the need for us to pay more attention," Stouffer said.