[Ed. – Uhh … what?]
Researchers analysed 70,716 specimens from 52 North American migratory bird species collected over 40 years.
The birds had died after colliding with buildings in Chicago, Illinois.
The authors say the study is the largest of its kind and that the findings are important to understanding how animals will adapt to climate change.
“We found almost all of the species were getting smaller,” said lead author Brian Weeks, an assistant professor at the school for environment and sustainability at the University of Michigan. …
The evidence suggests warming temperatures caused the decrease in body size, which in turn caused the increase in wing length.
“Migration is an incredibly taxing thing they do,” Mr Weeks said, explaining that the smaller body size means less energy available for the birds to complete their long journeys.