Migratory birds in North America are shrinking as their wings get bigger

[Still Waters]

North American migratory birds are becoming smaller as the planet warms due to climate change, a new study finds.

Researchers from the University of California, Los Angeles (UCLA) examined more than 30 years of data for adult male birds across 105 avian species that migrate through North America. They found that between 1989 and 2018 the birds' body masses declined by about 0.6% on average, according to an Oct. 27 study in the journal Nature Ecology and Evolution.

The species that "experienced the greatest change over time" was the tree swallow (Tachycineta bicolor), said study lead author Casey Youngflesh, a quantitative ecologist from UCLA and a presidential postdoctoral fellow in the Ecology, Evolution, and Behavior (EEB) Program at Michigan State University. In this songbird, known for its striking iridescent blue feathers, body mass dropped by nearly 3%. 

https://www.livescience.com/north-american-migratory-birds-shrinking

https://www.nature.com/articles/s41559-022-01893-x