The warmer temperatures have caused these animals to evolve, according to a new study conducted on 77 species of birds over the past 40 years, and published Friday in the journal Science Advances.

The researchers' hypothesis: less heavy and with larger wings, birds can fly more efficiently, while spending less energy.

Smaller wings that have to carry more weight require you to beat them faster, producing more body heat.

Greater pressure on food resources may also have affected their weight, according to the study.

"This is all happening away from direct human disturbance (like deforestation), in the midst of the world's largest rainforest," Vitek Jirinec, lead author of the study, told AFP.

According to him, these results thus underline the general effect of climate change caused by humans.

He and his colleagues analyzed data collected on more than 10,000 non-migratory birds captured, measured and released, over an area of ​​around 40 kilometers in Brazil.

They also used climate models that allowed them to determine that temperatures had increased by 1 ° C during the rainy season, and by 1.65 ° C during the dry season since 1966.

All of the species studied were found to have smaller body mass compared to 1980. And most species lost an average of 2% body mass each decade.

Concretely, a species of bird weighing on average 30 grams in the 1980s, today weighs about 27.6 grams.

“These birds do not vary greatly in size,” said Philip Stouffer, co-author of the study, in a press release.

"So when an entire population loses a few grams, it is significant."

The birds moving the highest were those most affected by this weight loss, compared to those staying closer to the ground.

However, the former are more exposed to warmer and drier conditions.

In addition, 61 species also saw the length of their wings increase, according to the study.

Its authors believe that a similar effect likely affects other species living elsewhere in the world.

"It definitely happens everywhere, and probably not just in birds," stressed Philip Stouffer.

© 2021 AFP