Wildlife Wednesdays: Shrinking Birds | weatherology°
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By: Meteorologist Megan Mulford
Updated: Feb 7th 2022

Wildlife Wednesdays: Shrinking Birds

A study published in the journal "Ecology Letters" determined the actual size of birds has been shrinking over time, and may be due to global temperatures rising and the overall warming climate. The research was led by scientists at the University of Michigan where they analyzed more than 70,000 birds from 52 North American migratory bird species collected between 1978 and 2016. The bodies of ALL 52 species shrank over the 38 year time period. It was also interesting to note, that the wingspan actually grew in size. Researchers suggested this is because the birds are being forced to adapt to the changing climate. Benjamin Winger, the study's senior author, questioned "Are they able to keep up with temperatures or are they lagging behind?"

The scientists for the study measured the birds' body size, body mass, wingspan, and the length of the lower leg bone. It showed that the lower leg bone shrank 2.4% across species. In addition, an average of 2.6% of their total mass was lost too. As mentioned, wing lengths across species increased by an average of 1.3%! According to Brian Weeks, lead study author, he mentioned that the species that had the greatest reduction in size had the biggest increase in wingspan. He further mentions that the bird specie, warblers, had the most dramatic change over time. 

Researchers are still unsure why wing lengths are growing while birds are shrinking in size overall. Weeks suspects that, as birds are getting smaller, it is harder for them to migrate. As a result, their wings are getting long to cope with their size decrease. Wesley Hochachka, an ecologist at the Cornell Lab of Ornithology in New York, guesses that birds are trying to adapt and keep up with their changing environment. He goes onto mention that climate change alters vegetation, so birds have nowhere to go but up, and soon that may also run out. If temperatures continue to rise, this will exceed the limit of bird species, which will result in evolutionary changes over time.