The study was done in North America. It was conducted by UCLA. The conclusions are striking. Migratory birds are getting smaller. The research was published in Nature Ecology and Evolution.
It happened over the past three decades. The body mass of 105 bird species decreased by as much as 3.0 %. Tree swallows, for example, declined by 2.8 %. And woodpeckers declined by 2.2 %. In evolutionary terms, these are dramatic changes in a very short time.
Casey Youngflesh is a UCLA (University of California Los Angeles) ecologist and lead author. “Climate change is literally shaping the appearance of species,” she said in a statement. “It’s a consistent signal across many species. There is no plausible hypothesis left except climate change.” Smaller bodies help animals cope with higher temperatures. The larger surface-to-volume ratio helps dissipate heat. Larger, rounder bodies are typical of birds in colder regions. They conserve heat better.
The size of birds varies predictably with location. In warmer places they have smaller bodies than in colder places. Birds in warmer locations became smaller at a faster rate. Even as the animals’ bodies shrank, their wings did not. It would be due in part to the fact that wings are not useful for regulating body temperature. “Wings are mostly feathers. Birds don’t use them to dissipate heat.”
The study presents the first large-scale evidence of another adaptation. Birds living at higher elevations tend to have longer wings. This helps them fly in the rarefied air of mountainous environments.
“Migratory birds are getting smaller. It’s surprising how species are changing in ways we didn’t think they would,” the researchers say. “The change doesn’t completely offset all the warming they’re going to experience.