Biology of Basal Birds and the Origin of Avian Flight

摘要

The protobirds were probably unable to forage on trees and take off from the ground because of a poor maneuverability of their wings and flight. The combination of ground foraging and necessity to use gravity for takeoff makes running to climb to the safety of heights the most likely escape strategy. The Climbing Escape Model proposes that passive flight originated as a sequel to emergency climbing and facilitated the return to ground foraging. Subsequently, powered (flapping) flight evolved to extend the flight path after takeoff from objects that by themselves were too low to secure protection against predators, thus making birds largely independent of the presence of safe heights (especially trees) in their feeding range. The life styles of Confuciusornis and Rahonavis may have been consistent with climbing as a prerequisite of takeoff in the basal birds.