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Study shows that Amazonian birds are shrinking due to climate change
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Study shows that Amazonian birds are shrinking due to climate change

Amazonian birds are shrinking in response to climate change, study shows


  • A new study has shown that birds in unaffected areas of the Amazon are developing smaller bodies and longer wings as a response to changing climate conditions.
  • Researchers found that 36 of the 77 species they studied had lost nearly 2% of their bodyweight per decade since 1980. 61 also saw an increase in their wing length.
  • Researchers link these morphological changes to climate change: with hotter temperatures and less predictable rainfall patterns, the birds are evolving to “eat less, get smaller, produce less heat.”
  • Climate change is a greater threat to South American birds than to birds in temperate climates.

The canary in the coal mine for how climate change is affecting the treasure trove of biodiversity in the Amazon is … also a bird. According to a, there are actually dozens of them. new studyThis shows that the changing climate is actually shrinking and lengthening their wings.

“Our findings show that man-made climate change, and therefore individual lifestyles of people around the world, manifests itself in something as fundamental as the body size and shape of birds in intact Amazon forest,” says study lead author Vitek Jirinec, a biologist with Brazil’s National Institute for Amazonian Research (INPA). “These results underscore the global part of climate change.”

The study, published in Science and presented at COP26 climate summit in Glasgow (Scotland) in November, examines how 77 Amazonian bird types have adapted to changing climate conditions over the past 40 years. Jirinec states that birds are a good indicator of environmental changes.

“Mammals usually have night habits and live sheltered, for example, in burrows. Birds are exposed. Additionally, they are relatively easy to observe and measure,” he says.

A collared puffbird (Bucco Capensis), one among the 77 species of birds studied. Vitek Jirinec.

Smaller birds

As quatro horas percorridas entre Manaus e o acampamento guardam quase sempre surpresas, como um tronco bloqueando a estrada rudimentar de terra. E lá descem os pesquisadores do veículo 4×4 para abrir o caminho.

For their study, Jirinec and his fellow researchers relied on a wealth of data gathered from one of the world’s longest continuously running research initiatives: the Biological Dynamics of Forest Fragments Project (BDFFP)The study was initiated by Thomas Lovejoy, a renowned conservationist and co-author of the most recent version.

At the project site, a four-hour drive from Manaus, the capital of the state of Amazonas, the researchers set up mist nets — very thin, 12 meters (40 feet) long — to capture birds. The researchers collected as much information as possible about each bird, including their weight and age, as well as data on them.

Vitek Jirinec, a researcher, with an Amazonian motmot (“Momotus Momota”). Phil Stouffer.

“The project has been [tagging] birds for 40 years, and I took part in different studies for four years, assessing several aspects related to birds,” says study co-author Bruna Amaral, a biologist at INPA and master’s student in ecology at Penn State University in the U.S. “Several generations of researchers have already worked on the bird project, and this is very difficult to achieve.”

Armed with their newly gathered data and the historical records made over the past 40 years, Jirinec, Amaral and the other researchers then set to work analyzing the 77 species of non-migratory birds that live in the forest’s understory, or within 2 meters (6 feet) of the ground.

Their main finding was that the average body mass of all species they studied had decreased since 1980. 36 of them had lost nearly 2% per decade. The wing length of 61 species, out of 77, increased at the same time.

“It’s 2% per decade and it doesn’t seem much, but in the scale of these birds, it’s a very big change and it’s a long-term change,” Amaral says. “As little as it looks, it is very hard to reverse it.”

The study also established the relationship between body mass and wing length to understand the general changes in the birds’ morphology and their aptitude for flying. Lighter bodies have longer wings, which means that they require less energy to fly. The conclusion was that changes in the climate are responsible for the physical changes to the birds’ bodies.

A researcher examines the wing a rufous-capped anthrush (Formicarius collma). Vitek Jirinec.

Unpredictable conditions are becoming more common

Even in the case of a primary forest area like the BDFFP study site, which doesn’t face pressure from deforestation, climate change has already made its mark. Data going back to 1966 show that the average temperature here since then has increased by 1° Celsius (1.8° Fahrenheit) in the wet season and 1.6°C (2.9°F) in the dry season. Rainfall patterns have also changed with rainfall increasing by 13% in the wet season and decreasing 15% by the dry season.

Tropical birds are more sensitive to environmental changes than birds from temperate regions, which can experience extreme swings between summer and winter. To cope with the tropical heat, they use water to regulate their body temperature — their late-afternoons baths in streams aren’t just for leisure; they’re also a matter of health.

Changes in precipitation that lead to less predictable rain and food availability can increase the stress levels of birds. The evolutionary response to this is to go light — and that seems to have been the birds’ strategy.

Common scale-backed antbird (Willisornis Poecilinotus), has lost an average of 1% per decade over the past 40 years. Cameron Rutt.

“Not being able to predict the amount of resources they will have leads the birds to try to preserve themselves by saving as much as possible,” Amaral says. “When you don’t have predictable access to resources, the strategy you have is to minimize the energy you use: eat less, get smaller, produce less heat.”

It is widely believed that climate change poses the greatest threat to birds in South America. This makes it difficult for them to adapt to changing environments or become more vulnerable. A 2020 studyThe paper was co-authored by many of the same researchers who wrote the recent paper. It details the decline in bird populations as a result climate change.

“The big challenge is to see how you turn this type of data or result into conservation, into public policies,” Amaral says. “We are accumulating a lot of knowledge, but we are not able to apply that knowledge to conservation in the same proportion. So it’s a little frustrating.”

During COP26 analysts showed that countries’ climate commitments to date will not be enough to cap global warming at 1.5°C (2.7°F) above pre-industrial levels by 2100.

Banner image of an Amazonian royal Flycatcher (Onychorhynchus Coronatus), one the 77 bird species that were analyzed in the new study. Philip Stouffer. 


Jirinec, V., Burner, R. C., Amaral, B. R., Bierregaard, R. O., Fernández-Arellano, G., Hernández-Palma, A., … Stouffer, P. C. (2021). Morphological effects of climate change for intact Amazonian rainforest birds. Science Advances 7(46). doi:10.1126/sciadv.abk1743

Stouffer, P. C., Jirinec, V., Rutt, C. L., Bierregaard, R. O., Hernández‐Palma, A., Johnson, E. I., … Lovejoy, T. E. (2020). Long‐term change in the avifauna of undisturbed Amazonian rainforest: Ground‐foraging birds disappear and the baseline shifts. Ecology Letters 24(2): 186-195. doi :10.1111/ele.13628

This story was reported by Mongabay’s Brazil team and first published hereOur website Brazil siteNovember 15, 2021


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