This study is super-duper interesting because it makes the connection between the presence of predators and not only the evolution of flightlessness but also the degree of 'power' (flight muscle development, leg length) for the still flighted birds (less predators, less power in the wings because they don't need to take off as quickly). I think one can draw conclusions on clipping from it...
https://www.sciencedaily.com/releases/2 ... 134949.htm




