As climate changes and gets warmer, birds are shrinking and their wingspans are growing, according to a new study.

The new study examined four decades of data on bird species and found that as the Amazon’s dry season has gotten hotter and more arid, some species appear to be changing physically.

According to a report by National Geographic, birds are often considered sentinel species—meaning that they indicate the overall health of an ecosystem—so scientists are particularly interested in how they’re responding to climate change. 

In general, the news has not been good. For instance, a 2019 report by the National Audubon Society found that more than two-thirds of North America’s bird species will be vulnerable to extinction by 2100 if warming trends continue on their current course.

A Science News article says - Over 40 years, dozens of Amazonian bird species have declined in mass. Many species have lost nearly 2 percent of their average body weight each decade, researchers report.

For the new study, researchers collected the biggest dataset so far on the Amazon’s resident birds, representing 77 non-migratory species. Suring the study period, the average temperature in the region rose, while precipitation declined. Temperatures increased by one degree Celsius during the wet season and 1.65° Celsius in the dry season. Precipitation increased by 13 percent during the rainy season but decreased by 15 percent in the dry season, making for a hotter, dryer climate overall.

These climatic changes overlapped with changes in the birds’ builds, the researchers say, with the dryer climate going further to explain the changes.

But the scientists aren't exactly sure why warmer temperatures cause birds to shrink.

“Climate change isn’t something of the future. It’s happening now and has been happening and has effects we haven’t thought of,â€_x009d_ says Ben Winger, an ornithologist at the University of Michigan, in an article published in Science News.

As per a BBC report, one theory is that smaller animals are better at cooling off, losing body heat more quickly due to their larger surface-area-to-volume ratios.

In 2014, researchers found that alpine goats appeared to be shrinking due to warming temperatures. The same year, another study found salamanders had shrunk rapidly in response to climate change.

(Banner image courtesy: commons.wikimedia.org)