Their wings, on the other hand, have lengthened over time.

Even the most pristine parts of the vast Amazon rainforest cannot escape it: climate change. A new study shows that not only has the number of vulnerable birds in the Amazon declined, but most species are also physically changing. “Even in the midst of the pristine Amazon rainforest, we can see the global impacts of human-induced climate change,” said study researcher Vitek Jirinec.

Study

The scientists studied data from more than 15,000 birds living in the world’s largest rainforest, captured, measured and weighed over the past four decades. It leads to a striking discovery. The data shows that almost all birds have shrunk and become a bit lighter since the 1980s. In contrast, their wings have grown.

Researchers measure the wing length of a thrush ant pitta. Image: Vitek Jirinec

The dataset covers a large part of the rainforest, the researchers write. This means that the physical changes the birds have undergone are not tied to one specific place, meaning the phenomenon is ubiquitous.

Lighter

The researchers found that most bird species have lost about two percent of their body weight per decade on average. This means that a bird species that weighed 30 grams in the 1980s now only has 27.6 grams. While this may seem like a subtle anomaly, the researchers say it’s significant. “If everyone in the population gets a few grams lighter, that’s a significant difference,” said researcher Philip Stouffer.

birds

However, the question is why exactly these physical changes occur. The scientists therefore examined 77 bird species that live in different parts of the rainforest. Some stay close to the cool, dark forest floor while others live in the warmer, sun-drenched middle section. The team found that the birds most exposed to heat and dry conditions also had the greatest physical changes — in body weight and wing length. Moreover, these birds seem to fly more than the birds that live on the forest floor.

Energy efficient

What does this have to do with climate change? It appears that the birds have adapted to a hotter, drier climate by reducing their wing loading, allowing them to fly more energy-efficiently. That’s right. A fighter jet has a fairly heavy body and short wings, so it needs much more energy to move fast than a glider with a slender body and long wings. If a bird has a higher wing load, it must flap its wings faster to stay in the air. Not only does this cost more energy, but it also produces more metabolic heat. Reducing body weight and increasing wing length is therefore a lot more efficient. And at the same time they also keep their bodies cool in this way.

Other animals

The research indicates that there appears to be a causal relationship between the warming planet and the body size and wing length of birds in the Amazon rainforest. It means that these animals are responding to their changing habitat. And probably birds aren’t the only ones transforming. “This is definitely happening everywhere,” Stouffer says. “If you look out your window, the conditions are not the same as 40 years ago. And it is very likely that plants and animals will respond to those changes.”

Good or bad?
You might think that these observed transformations are good news. Birds seem to be successfully adapting to the future warmer climate. However, according to scientists, it is still difficult to say whether it is something good or bad. On the one hand, it indeed implies that animals evolve in response to climate change and thus try to survive. On the other hand, we do not yet have data to confirm that the observed physical changes actually help populations to survive. Physical change does not mean that animals deal with climate change and that all is well. It simply means that they evolve to survive. Whether that works is another matter.

We know that climate change has winners and losers. On the one hand are the animals that successfully adapt to changes in their living environment and in this way secure their future. On the other hand, climate change has losers; the animals that bounce too slowly and thus approach their demise. Whether the birds in the Amazon rainforest will manage to cope with increasingly warmer and drier environments remains to be seen.