Birds keep a layer of soft, fluffy down feathers to regulate body temperature
Feathers are a sleek, intricate evolutionary innovation that makes flight possible for birds, but in addition to their stiff, aerodynamic feathers used for flight, birds also keep a layer of soft, fluffy down feathers between their bodies and their outermost feathers to regulate body temperature.
Using the Smithsonian's collection of 625,000 bird specimens, Sahas Barve, a Peter Buck Fellow at the Smithsonian's National Museum of Natural History, led a new study to examine feathers across 249 species of Himalayan songbirds, finding that birds living at higher elevations have more of the fluffy down--the type of feathers humans stuff their jackets with--than birds from lower elevations.