Climate Change Might Be Making Tropical Birds Smaller

Gillian Sisley

This is an incredible example of nature adapting to crisis.

Brazil's Amazon rainforest has been the hub of some exciting research. In the last decade, scientists have been measuring birds relatively untouched by deforestation and roads. They have spent their time in the climate gathering data to find out how habitat fragmentation, such as logging and the increase of industrialization such as roadwork, can affect the general biology of the species living in relatively untouched conditions.

With industrialization all over the globe affecting most wildlife, a surprising discovery has been made -- birds living deep within the Amazon rainforest are getting smaller.

The research from these wilderness experts shows that, over the last 40 years, birds in the Amazon have been declining in mass, with many species having lost almost 2% of their average body weight with each passing decade.

Results published on November 12th in Science Advances found that birds shrinking also overlaps with data indicating hotter and more variable climates in the Amazon rainforest. What this indicates to researchers is that the birds are getting smaller so that they can have more efficient bodies that can stay cooler in an increasingly hotter climate.

These findings align with what we already know about size and temperature in the animal kingdom.

Biologists have concluded for some time now that body size and temperature are directly linked. For example, it is more beneficial to be larger in cooler climates, as less heat is lost with larger mass.

That said, research finds that many species of North American migratory birds are getting smaller, as published in a 2020 Ecology Letters report. The data from the research published in Science Advances backs this up, finding that bird biology measurements such as mass and wing length taken from 1979 to 2019 over 11,000 bird species have indicated this shrinking taking place across the board. Climate data from the same area was taken and compared along with the measurements.

With all species declining in mass, these changes coincided with an average 1 degree celsius temperature increase in the wet seasons, as well as 1.65 degrees celsius increase in the dry seasons.

Weather isn't the only factor to blame.

Temperature shifts aren't the only factors that were noted in the report. Decreased food availability is another possibility for the smaller size. That said, researchers did note that the different species documented had differing diets, thus the more pervasive and likely cause for their decline in size is climate change.

It is unclear whether these changes in size and shape represent a definitive evolutionary adaptation to climate change, or perhaps a physiological shift due to warmer temperatures. Regardless, increased human activity on a global level remains to be one of the contributing players in either theory.

Vitek Jirinec, an ecologist at the Integral Ecology Research Center, stated about the study to Science News:

“The Amazon rainforest is mysterious, remote and teeming with biodiversity. This study suggests that even in places like this, far removed from civilization, you can see signatures of climate change.”

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