Duh, Climate Change Makes Birds Shrink in Size

 


The researchers found surprising facts related to the impact of climate change. They found birds in the tropics experienced a decrease in body size.

The findings were revealed in scientists at Science Advances a few days ago. The scientists have been capturing and measuring birds in the Amazon forest for decades that have not been damaged by deforestation.


Over the past 40 years, dozens of bird species in the Amazon jungle have declined en masse. Many species have lost nearly 2 percent of their average body weight each decade.


What's more, some species have longer wings. The change is believed to be due to a hotter climate, the shrinkage making for a leaner and more efficient body to help birds stay cool, the researchers said.


"Climate change isn't something in the future. It's happening now and it's happening and it's having effects we never thought about," said Ben Winger, an ornithologist at the University of Michigan in Ann Arbor who wasn't involved in the study but has documented similar shrinkage in birds. who migrated.


Biologists have long linked body size and temperature. In colder climates, being bigger is beneficial to reduce heat loss through the skin and keep the body warm.


"As the climate warms, body size shrinks to help organisms better release heat," said Vitek Jirinec, an ecologist at the Center for Integral Ecology Research in Blue Lake, California.


Many species of North American migratory birds are getting smaller, Winger and colleagues report in 2020 in Ecology Letters. Climate change is a possible cause, Winger said, but because migrants experience a variety of conditions while exploring the world, other factors such as degraded habitat that birds may encounter cannot be ruled out.


To see if habitation birds have also dwindled, Jirinec and colleagues analyzed nonmigratory bird data collected from 1979 to 2019 in the Amazon region spanning 43 kilometers. The dataset includes measurements such as mass and wing length taken from 1979 to 2019 for more than 11,000 individual birds of 77 species. The researchers also examined climate data for the region.


All species declined en masse during this period, the researchers found, such as the rufous-capped warbler, which ate insects from the forest floor, and the Amazonian mothmot, which ate fruit on trees. Species lose from about 0.1 percent to nearly 2 percent of their average body weight each decade. Motmot, for example, shrunk from 133 grams to about 127 grams during the study period.


This change coincided with an increase in average temperature of 1 degree Celsius overall in the rainy season and 1.65 degrees Celsius in the dry season. Temperature and precipitation also become more variable over time.


"The dry season is really stressful for the birds," says Jirinec. Bird mass declines most in the year or two following a hot, dry season, which is in line with the idea that birds are getting smaller to cope with heat stress.


Other factors, such as decreased food availability, can also lead to smaller sizes. But because birds with very different diets all experience mass decline, climate change is likely to be the cause, Jirinec said.


The researchers found that the wingspan in 61 species experienced a maximum increase of about 1 percent per decade. Jirinec thought that the longer wings made the flyer more efficient, and thus cooler.


For example, fighter jets, with their heavy bodies and compact wings, require enormous power to maneuver. On the other hand, a light glider with long wings can move around much more efficiently.


"Longer wings might help [birds] fly more efficiently and produce less metabolic heat, which could be beneficial in hotter conditions. But that's just a hypothesis. These body changes are most pronounced in birds that spend their time higher up in the canopy, in where conditions are hotter and drier than the forest surface," Jirinec said.


Whether this change in shape and size is an evolutionary adaptation to climate change, or simply a physiological response to warmer temperatures, remains unclear. Whatever the case, Jirinec points out that change demonstrates the destructive power of human activity.


"The Amazon rainforest is mysterious, remote and full of biodiversity," he said. "This study shows that even in places like this, far from civilization, you can see signs of climate change."

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