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As average summer temperatures rise, North American birds are getting smaller, according to a study of 70,716 specimens published yesterday (December 4) in Ecology Letters.
David Willard, a collections manager emeritus at the Field Museum in Chicago and a coauthor of the study, has been collecting and measuring birds that died by crashing into Chicago buildings for more than four decades. He and a team of researchers analyzed specimens collected from 1978–2016 that represent 52 common bird species, mainly sparrows, warblers, and thrushes. They found that during the past few decades, body mass decreased by 2.6 percent, leg bones shortened by 2.4 percent, and wing length increased by 1.3 percent on average.
The scientists don’t know why birds are shrinking, but they say they believe that it could be because smaller animals keep cool more easily, or because warm temperatures can stunt the growth of young ...
