High-altitude birds evolved thicker 'jackets' By Victoria Gill image copyrightAditya Chavan A study of 250 species of Himalayan songbirds has revealed how their feathers evolved for higher altitudes. The birds in colder, more elevated environments had feathers with more fluffy down - providing them with thicker "jackets". The insight reveals how feathers provide the tiniest birds with such efficient protection from extreme cold. It also provides clues about which species are most at risk from climate change, the scientists say. image copyrightVictoria Gill "It was just zipping around catching bugs." Dr Barve's fingers went numb as he tried to take notes.