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Birds Are Shrinking Because of Climate Change, Study Finds

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Dec 6, 2019

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Earlier research suggests the Arctic red knot is also shrinking in size. This is a projection comparing the red knot's current size and it's probably size in the future. (Image Credit: Jan van Gils, NIOZ)

Birds are shrinking due to warming temperatures caused by climate change, according to a study of 40 years’ worth of specimens from 52 North American migratory species.

“We found almost all of the species were getting smaller,” lead author Brian Weeks, Ph.D. and an assistant professor at the University of Michigan in the U.S., told the BBC. “The species were pretty diverse, but responding in a similar way. The consistency was shocking.”

(Looks like humans may have hope for surviving the bird apocalypse yet.)

Weeks suggests birds’ bodies have shrunk in order to help them cool more efficiently in warming temperatures. But smaller bodies produce less energy — a problem for these species, which go through highly taxing seasonal migrations that span thousands of kilometers. Bird body sizes have shrunk by roughly 2.4% over the past decade (as determined by the length of the lower leg bone, a common way to estimate whole body size). Interestingly, to compensate for that, birds’ wingspans have grown by 1.3%.


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The study, published in the journal Ecology Letters, is the largest of its kind to look into animals’ physical changes in response to climate change, which is an underresearched field. Most studies examine how climate change affects animals’ migratory patterns or habitat and life cycle timings around birth and migration.

However, it is not the only study to examine how climate change affects animal size. Smaller, previous studies corroborate Weeks’s findings. Earlier this year, a study from the University of Cape Town found mountain wagtails, a type of bird native to sub-Saharan Africa, have shrunk in average weight over a 23-year period, which the researchers attributed to warming temperatures. Studies of animals as diverse as Arctic red knots and zebra finches to beetles to mountain goats to fish have led to similar conclusions.

“I find it very interesting — or concerning, depending on which way you look at it,” Alan Baudron, a biology research fellow at the University of Aberdeen, told Gizmodo’s Earther in 2018. “Across different species in different environments, with different life-history characteristics — such as cold-blooded and warm-blooded — there seems to be a general trend that the size is shrinking.”

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Written By Liesl Goecker

Liesl Goecker is The Swaddle’s managing editor and has been living and writing in Mumbai since 2010. She is passionate about women’s rights, everyone’s health, and caffeine.

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