Earlier this year in National Geographic, I wrote about how feathers evolved long before flight. This timing naturally raises the question, how did feathered dinosaurs take to the air? My article was accompanied by a picture from the University of Montana lab of Ken Dial, who argues that before dinosaurs flew, they flapped their wings to help them travel up and down inclines. While not all experts accept Dial's hypothesis, it has the undeniable strength that he can gather evidence for it in living birds, rather than just inferring behavior from fossils alone. This video shows some of the astonishing climbs birds can make with the help of some wing flapping. It's a mix of lab climbs and footage from the wild, with an evolutionary tree of birds. http://www.youtube.com/watch?feature=player_embedded&v=VFUNhTdcNdk#! This is a skill that takes time for birds to develop, as shown in this video below. Dinosaurs might have gradually acquired the skill as well, as their arms evolved into more bird-like wings. Dial argues that this flapping would also help on the way down, too. Here's a young bird leaping to the ground, and flapping its wings to control its fall. By the time dinosaurs had evolved the ability to use feathers to assist in climbs, they would have already developed the wing stroke used by birds today for true flight, as this video shows. Even without full flight, Dial argues, flapping feathered wings would have given little feathered dinosaurs the boost they needed to escape hungry predators. And this behavior could have served as an evolutionary bridge from the land to the air.
Tip of the maniraptoran hat to Tom Holtz