Above the Amazon rainforest canopy where birds have become smaller and their wings have become longer over several generations, indicating a response to the shifting environmental conditions that may include new physiological or nutritional challenges.
Photo credit: Vitek Jirinec, LSU
A study by a combined team from the USA, Brazil and Portugal, led by Vitek Jirinec of Louisiana State University's School of Renewable Natural Resources, has found evidence that climate change is causing birds of the Amazon Rainforest to evolve smaller bodies and longer wings, even in the areas of the forest where human activity is minimal.
They arrived at this conclusion by examining data from measuring over 15,000 birds over a period of 40 years from a wide range of sites. Over that time the body mass of individuals has reduced by about 2% per decade, so that a bird species with an average body weight of 30 grams in 1980 would now have an average weight of 27.6 grams. These changes are not confined to specific areas, so eliminating local factors. In other words, the changes are being produced by a pervasive environmental change.
The team have published their findings, open access a few days ago, in Science Advances.
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.
This is undoubtedly happening all over and probably not just with birds...If you look out your window, and consider what you’re seeing out there, the conditions are not what they were 40 years ago and it’s very likely plants and animals are responding to those changes as well. We have this idea that the things we see are fixed in time; but if these birds aren’t fixed in time, that may not be true.
Where there was a significant difference, however, was related to the level in the forest that the species normally inhabits, from the forest floor to the canopy. The change was most marked in those which occupy the higher levels, where climate change has had the biggest impact making it drier and hotter. This has created an environment which favour lighter bodies with longer wings, both of which improve flight efficiency so making it easier to tolerate higher temperatures.This is undoubtedly happening all over and probably not just with birds...If you look out your window, and consider what you’re seeing out there, the conditions are not what they were 40 years ago and it’s very likely plants and animals are responding to those changes as well. We have this idea that the things we see are fixed in time; but if these birds aren’t fixed in time, that may not be true.
Professor Philip Stouffer, co-author
Lee F. Mason Professor
School of Renewable Natural Resources
Louisiana State University, Baton Rouge, LA, USA
Lee F. Mason Professor
School of Renewable Natural Resources
Louisiana State University, Baton Rouge, LA, USA
In the abstract to their open access paper, published in Science Advances, the authors say:
AbstractThis is a clear example, not only of the effects of climate change but of how significant environmental change can influence the evolution of species as the environment selects for those characteristics which give greater fitness. It's a beautiful example of how science quite incidentally and with no intention on the part of the authors to do so, casually refutes Creationism by revealing the facts and so confirming once gain how evolution by natural selection works in practice. Significant morphological changes have occurred in these species over a defined time period and that change is proportional to the impact of a pervasive, measurable environmental change in different ecological niches.
Warming from climate change is expected to reduce body size of endotherms, but studies from temperate systems have produced equivocal results. Over four decades, we collected morphometric data on a nonmigratory understory bird community within Amazonian primary rainforest that is experiencing increasingly extreme climate. All 77species showed lower mean mass since the early 1980s—nearly half with 95% confidence. A third of species concomitantly increased wing length, driving a decrease in mass:wing ratio for 69% of species. Seasonal precipitation patterns were generally better than temperature at explaining morphological variation. Short-term climatic conditions affected all metrics, but time trends in wing and mass:wing remained robust even after controlling for annual seasonal conditions. We attribute these results to pressures to increase resource economy under warming. Both seasonal and long-term morphological shifts suggest response to climate change and highlight its pervasive consequences, even in the heart of the world’s largest rainforest.
Copyright: 2021 The authors. Published by American Association for the Advancement of Science.
Open access
Reprinted under a Creative Commons Attribution-NonCommercial 4.0 International license (CC BY-NC 4.0)
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