Why Are Birds in the Americas Getting Smaller? Scientists Think Global Warming Could Be the Culprit

Researchers led by the University of Michigan found that birds in the Americas are experiencing changes due to global warming. Birds are becoming smaller in body size and longer in wing length, wherein the smallest species of birds are undergoing the most significant changes.

They reported the findings of their study, titled "Body Size Predicts the Rate of Contemporary Morphological Change in Birds," in the Proceedings of the National Academy of Sciences.

Why Are Birds in the Americas Getting Smaller? Scientists Think Global Warming Could Be the Culprit Pixabay/Pexels

Smaller Birds Are Evolving Faster

According to Science Daily, the study combines data from two previously published studies, one conducted in Chicago and the other in the Amazon, that measured body size and wing-length changes in more than 86,000 bird specimens over four decades.

Despite variations in species mix and data collecting techniques, both studies found that body size decreased while wing length increased. Smaller bird species dropped proportionally quicker in body size and expanded proportionately faster in wing length in both trials. The specific reason why smaller-bodied animals change quicker is unknown, but the researchers speculate that smaller-bodied birds may adapt to evolutionary forces more quickly.

However, the available data did not allow the team to test whether the observed size shifts represent rapid evolutionary changes in response to natural selection.

Both studies attribute the reductions in species' body size to increasing temperatures over the past 40 years, suggesting that body size may be an important determinant of species' responses to climate change.

The findings of the study also suggest that body size is a significant modulator of birds' reactions to current climate change. More research is needed to establish the biological mechanism behind the observed relationship between body size and morphological change rates.

Birds' Body Size May Predict Risk of Extinction

As per a similar report from Phys.org, the combined data from both studies shows that researchers were able to collect 86,131 specimens from 129 species from roughly the same period using different techniques.

They measured body size and wing-length changes in more than 86,000 bird specimens in North and South America, revealing that smaller bird species declined proportionately faster in body size and increased proportionately faster in wing length.

According to the study's authors, big body size may worsen extinction risk by reducing the ability to adjust to rapid, continuing anthropogenic change, and body size appears to be a significant modulator of birds' reactions to current climate change.

However, if smaller-bodied bird species are evolving faster, it may increase their persistence if their rapidly changing morphology reflects a faster adaptive response to changing conditions.

The researchers investigated whether two fundamental organismal features, body size and generation duration, influenced birds' reactions to fast environmental change. They identified no relationship between generation time and rates of change in North American bird species after controlling for body size.

However, in both the Chicago and Amazonian birds, the mean body size of a species was strongly related with the rates of change recorded. According to the scientists, body size may be a useful predictor of adaptive capability and the amount to which modern evolution may minimize the danger of extinction among species.