A study published Wednesday involving 70,716 birds killedfrom 1978 through 2016 in such collisions in the third-largestU.S. city found that their average body sizes steadily declinedover that time, though their wingspans increased.
The results suggest that a warming climate is driving downthe size of certain bird species in North America and perhapsaround the world, the researchers said. They cited aphenomenon called Bergmann’s rule, in which individuals within aspecies tend to be smaller in warmer regions and larger incolder regions, as reason to believe that species may becomesmaller over time as temperatures rise.
The study focused on 52 species mostly songbirds dominatedby various sparrows, warblers and thrushes that breed in coldregions of North America and spend their winters in locationssouth of Chicago. The researchers measured and weighed a paradeof birds that crashed into building windows and fell to the ground.
Over the four decades, body size decreased in all 52species. The average body mass fell by 2.6%. Leg bone lengthdropped by 2.4%. The wingspans increased by 1.3%, possibly toenable the species to continue to make long migrations even withsmaller bodies.
“In other words, climate change seems to be changing boththe size and shape of thesespecies,” said biologist Brian Weeksof the University of Michigan’s School forEnvironment andSustainability, lead author of the study published in thejournal Ecology Letters.
“Virtually everyone agrees that the climate is warming, butexamples of just how that is affecting the natural world areonly now coming to light,” added Dave Willard, collectionsmanager emeritus at the Field Museum in Chicago, who measured allthe birds.
The study provides fresh evidence of worrisome trends forNorth American birds. A study published in September documenteda 29% avian population drop in the United Statesand Canadasince 1970 and a net loss of about 2.9 billion birds.
“I think the message to take away is this,” Weeks said. “Ashumans change the world at anunprecedented rate and scale,there are likely widespread and consistent bioticresponses toenvironmental change.”
Get real time update about this post categories directly on your device, subscribe now.