Evanildo da Silveira – De Vera Cruz (RS) for BBC News Brasil
posted on 11/14/2020 13:40 / updated on 11/14/2020 13:40
In theory, untouched regions and far from human interference in a tropical forest do not come to mind as a place where one would expect to find a decline in populations of bird species or any animals.
But this is exactly what a long-term study – over 35 years – carried out by American researchers, found in undisturbed areas of the Amazon.
They found that birds that feed on insects in the soil and others that live in the lower parts of the forest are disappearing from these areas. And they suggest that the phenomenon is being caused by climate change.
The study is part of the Biological Dynamics of Forest Fragments Project (PDBFF), created by American biologist and environmentalist Thomas Lovejoy, in 1979, and which has since been operating in an area of untouched forest, 80 km north of Manaus.
Between 2008 and 2016, biologist Philip Stouffer, from the Department of Natural Resources at Louisiana State University (LSU), led a group that repeated the work that had been done between 1980 and 1984 by his fellow countryman, the zoologist Rob Bierregaard, who directed the project in the first eight years of its existence.
In an interview with BBC News Brasil, Stouffer said that the objective of his work was to capture an adequate sample of bird species, in the same area that Bierregaard collected, to compare their abundance with the 1980-1984 data.
“We noticed that around 2008, terrestrial insectivores became more difficult to find than at the time of the previous study”, he explains.
“We then decided to test the hypothesis. It took us years – until 2016 – to accumulate data from 21 sites, in a 40 km strip of forest, to compare with the 34 in the 1980s.”
The samples from both works were collected using exactly the same method.
“We use lines of fog nets (special nets used to capture birds and bats for scientific purposes, almost invisible to animals) 200 meters wide by 2.5 meters high, to passively capture birds – without bait or something to attract them, “says Stouffer.
“It is thus easy to standardize the effort and there are no identification problems with the birds in hand. We observed that a group that uses the ground or the lowest vegetation has reduced abundance, compared with data from the same forest in 1980-1984.”
According to Stouffer, the most important conclusion of the research, “and terrible for biodiversity”, is that birds specialized in feeding on the ground are less common than they were.
“(The worst) is that this is happening without disturbance of the landscape, such as, for example, fire, fragmentation of the forest or invasive species, which are the typical threats”, he says.
“In other words, the results indicate that, even in the intact forest, there is a loss of biodiversity.”
In numbers, the study shows that of the 79 species captured and studied, 52 showed declining populations; 24, increase; and three remained stable.
“Among those that had the greatest reduction in the number of individuals is the red-bellied chock (Isleria guttata), which had been registered in 59% of the sites surveyed in 1980-1984 and is now found only in 14% of the sites studied “, reveals biologist Cameron Rutt, now a postdoctoral researcher at George Mason University, who was a student of Stouffer and participated in the study when he was at LSU.
The brown leaf turner is also on the list (Sclerurus caudacutus), from 53% to 10%; the uirapuru-real (Cyphorhinus plow), from 59% to 29%; the white-winged uirapuru (Microcerculus bambla), from 50% to 19%; the pinto-do-mato-carijó (Myrmornis torquata), from 47% to 19%: “In fact, even though I spent a year and a half doing field research in the area, I never saw the brown leaf-turner,” he says. Rutt.
“Despite these specific birds, which registered a great decline, when only the statistically relevant results are considered, of the 79 studied, only 17 underwent changes, 9 in decline and 8 with increase”, explains Rutt.
That is, there is a similar number of species in decline compared to those that are increasing.
Therefore, one might think that this is a random, natural and unimportant result. But it is not.
What makes the discovery of the new study impacting and worrying is the place where it was made: an area of untouched forest.
Researcher Mario Cohn-Haft, from the Department of Biodiversity (COBIO) and Zoological Collections – Birds, from the National Institute for Research in the Amazon (Inpa), explains why.
“If they were simply random changes, this variation would be expected, some species in decline and others in ascension”, he says.
“What makes the difference is that the researchers found that what was expected to happen in areas of forest degradation has occurred.”
According to him, the species that have decreased are the same that would fall in altered areas. And those that have increased are those that would benefit from the destruction of the forest, because they are opportunists and have a better capacity to adapt to environmental changes.
“This is strong evidence that the change in time is in the same direction as when there is degradation and fragmentation of the forest”, he explains.
In other words, they are not random changes, thus reflecting a pattern of forest degradation.
“Those species most sensitive to change are precisely those that have declined,” says Cohn-Haft.
“While those that have increased are those that benefit from the opening of the forest, an increase in temperature and light. Usually it is the birds that eat fruit. This suggests that the conditions of the forest are not being as stable as one imagines, that it is degrading in some way, with changes in the microclimate inside. Which strengthens the idea that the macro-climatic changes, that is, global, that go in the direction of heating and drying, are deeply influencing the interior of the Amazon rainforest. “
Although they still don’t know for sure what the cause of the phenomenon is, researchers have a chance.
“In this paper, we describe the pattern of declines and increases, but we still don’t know what may be the cause of these reductions,” admits Rutt.
“But at this point, our assumption is that what we are seeing is linked to events caused by global climate change. The mechanism may be a change in insect populations, which live in the soil (which birds eat), a change in structure of the forest, or something else. Of course, more research is needed to understand why these invisible losses are happening in the largest tropical forest in the world. “
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