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North American Birds' Bodies Shrinking, Wings Growing, Study Finds

Reuters

   WASHINGTON - Since 1978, researchers havescooped up and measured tens
   of thousands of birds that diedafter crashing into buildings in Chicago
   during spring and fallmigrations. Their work has documented a shrinkage
   in the size of the creatures.

   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.

   Mostly songbirds

   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.

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