The Amazon Rainforest is one of the most biodiverse locations on Earth, home to more than 3 million different species. It is also an important environmental asset to the planet, once working as a carbon sink to prevent excessive amounts of carbon dioxide from lingering in the air. Sadly, so much of the rainforest has been affected by some aspect of human action: increasing temperatures, droughts, deforestation, and increasing numbers of wildfires. As a result, almost 17% of the rainforest area has been lost over the past 50 years. This has affected wildlife in a number of ways, including habitat destruction.
But according to a new study published in Science Advances, not even species living in the most remote regions of the rainforest (that is, areas far removed from human contact) are free of the effects of human activity.
Using data collected over nearly 40 years, researchers tracked and studied different bird species (amounting to about 15,000 individual birds and 77 species studied). The data suggests that not only have bird species reduced in number, but that the species observed over this time period exhibited literal physical changes, namely in size and wingspan. Specifically, researchers indicated that birds have gotten small while their wing spans have grown wider, suggesting that these are some kind of evolutionary response to environmental changes, a concept known as Allen's rule.
“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,” said co-author Philip Stouffer.
Researchers covered a wide swatch of the rainforest, highlighting that these changes are not isolated findings, but are rather a quite pervasive phenomenon. Speculating on a potential cause for these changes, researchers noted that birds who had more exposure to hot, dry conditions (e.g., those living in the midstory or above) had the most significant changes in their physical size. As a result, researchers suspect that this may be a way to reduce the amount of effort it takes to fly in these hotter climates, allowing the birds to be more efficient flyers.