Even the most remote areas of the Amazon, where humans have not yet arrived, are being affected by climate change, new research reveals.
The hottest and driest conditions in the past four decades are shrinking the body size of rainforest birds while increasing their wing span, according to the study published in the journal Science Advances.
These changes are believed to be a response to nutritional and physiological challenges, especially during the dry season, which takes place between June and November.
“In the midst of this pristine Amazon rainforest, we are seeing the global effects of human-caused climate change,” Vitek Jirinec, an ecologist at the Center for Integral Ecology Research, a US-based non-profit organization, said in a statement.
Jirinec and his colleagues analyzed data collected on more than 15,000 birds that were captured, measured, weighed and tagged over a period of 40 years of fieldwork.
Researchers have found that nearly all of them have gotten lighter since the 1980s.
Most species have lost an average of 2% of their body weight each decade, meaning that a bird species that weighed 30 grams in the 1980s now weighs 27.6 grams on average.
Furthermore, the data did not correspond to a specific place, but were collected from a wide variety of areas of the rainforest, which means that the phenomenon could be verified everywhere.
In total, the scientists investigated 77 species whose habitats range from the dark and moist forest floor to the intermediate layer of forest vegetation, which receives the greatest incidence of light.
Birds in the higher layers, which fly more and are more exposed to heat, recorded the most pronounced changes in body weight and wingspan.
The team considered the hypothesis that it was an adaptation to energy pressures, for example, the decrease in the availability of resources such as fruits and insects, and also to thermal stress.
The longer wings and reduced weight-to-wing ratio produce more efficient flight, similar to that of a glider, which can fly using less energy.
A higher wing-weight ratio requires birds to shake their limbs faster to stay airborne, using more energy and producing more metabolic heat.
These species “are very much in tune with each other, so when everyone in the population is a few grams smaller, that’s significant,” said research co-author Philip Stouffer of Louisiana State University.
However, how well Amazonian birds can cope in the future with increasingly hot and drier conditions remains unanswered.
The authors added that it is likely that the same effect they recorded is also happening in other species around the world that live in extreme environments.
“Without a doubt, this is happening everywhere and probably not just with birds,” says Stouffer.
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