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Amazon rainforest birds are being transformed by climate change

In response to the pressures of climate change, birds rarely glimpsed by humans are losing weight and their wingspans are increasing in size, all in an effort to stay cool.

(CN) — Climate change is taking a toll on wildlife in some of the most remote regions on Earth, such as deep in the Amazon rainforest where tree canopies often blot out the sun and roads can be hard to come by.

Even amongst one of the planet’s premier examples of pristine wilderness, scientists can measure the impacts inflicted by climate change on animals that otherwise live lives mostly devoid of human contact. Assessing those impacts takes time, however, requiring long term monitoring of elusive species to track changes in their populations across years and decades.

A team of scientists from Louisiana State University led by Vitek Jirinec, an LSU alumnus and now associate ecologist at the Integral Ecology Research Center, found that a number of sensitive resident bird species throughout the Amazon rainforest have declined in number, while their bodies have tried to compensate for the increasingly warm weather. The authors published their results Friday in a new study in the journal Science Advances.

“Climate change can be connected to these subtle changes occurring in the middle of what we think to be the most pristine rainforest on the planet,” said Philip Stouffer, the Lee F. Mason Professor in the LSU School of Renewable Natural Resources, in an email. “What is less clear is if the altered morphology allows birds to manage changing conditions or if the trajectory of climate change will lead to ever more dramatic changes to rainforest plant and animal communities.”

Stouffer led field research trips into the Amazon rainforest north of Brazil since 1991 when he was a postdoctoral researcher with the Smithsonian, until his recent retirement from field work in the region. Beginning around 2008, Stouffer and his graduate students, including Jirinec, began to notice a number of changes in the resident birds there, such as certain species they once spotted with relative ease becoming ever more elusive.

To track down the cause, the authors analyzed data collected from over 15,000 individual birds over the past 40 years to determine what was going on. Among the species researchers looked at, they found the average individual’s body size decreased, while wingspans grew longer. The team focused on non-migratory birds to ensure their data would be tailored to species who inhabit the rainforest year-round.

They found that most of the birds studied, on average, lost around 2% of their body weight since the 1980s; a species that once averaged 30 grams now averages a bit less than 28 grams.

“These birds don’t vary that much in size. They are fairly fine-tuned, so when everyone in the population is a couple of grams smaller, it’s significant,” Stouffer said in a related statement. “This is undoubtedly happening all over and probably not just with birds. If you look out your window, and consider what you’re seeing out there, the conditions are not what they were 40 years ago and it’s very likely plants and animals are responding to those changes as well.”

The authors studied 77 species of rainforest birds, some preferring the cooler, darker region nearest the forest floor, while others spend their time in the sundrenched midstory region nearer to the canopy. They found the greatest change to body weight and wing length occurred in those species living in the upper levels of the midstory where the days are hottest and driest. The authors believe these changes are likely brought on by a need to reduce energy consumption, as these birds fly more than those living nearer to the forest floor.

Similar to how a large jet aircraft uses more energy to stay aloft than a lightweight glider — a heavier bird has to flap its wings more often during flight and generates more metabolic heat than a lighter bird with longer wings. Thus, increasingly hot weather may be leading certain species to shed weight and grow longer wings in an effort to reduce energy consumption and stay cool.

“The biggest surprise was how consistent the changes were,” Stouffer explained in an email. “We went into this study thinking we might reveal something happening to a suite of birds we know to be less abundant now than they were in the 1980s, even in pristine forest. What we found was an almost universal trend for lighter birds with longer wings.”

As for next steps, Stouffer said the team is studying how birds use microhabitats within the forest to avoid hot, dry areas, which is part of lead author Jirinec’s dissertation work. Stouffer hopes his colleagues will continue the long-term monitoring of rainforest birds now that his days in the Amazon are behind him.

“I need to thank all the people involved in the project since the 1970s,” Stouffer said. “Beyond the authors of the paper, there were many collaborators in Brazil who kept the project moving.”

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