One of these, dubbed the arboreal model, holds that it developed in a tree-dwelling ancestor that was built for gliding but started flapping to extend its air time.

• 一个浑名树栖模型，大意如下：鸟类祖先原来是树栖动物，本来就会滑翔，后来为了延长在空中停留的时间，才开始以翅膀上下拍扑。