Limitations of bird flight as an aircraft design What is it that stops man from duplicating Bird Flight as Engineering? 

After all, birds do not require separate propullsion! They use the same wings for propulsion and navigation. 

My question could be broad. Is it far-fetched ?

With solar energy harnessed and electronic control systems, SHOULD we not take a re-look at bird flight, at least as personal carriers or even as a short-haul option ?
The movement of the bird wing during the flight is very complex. Not just the trajectory matters, the shape of the wing itself changes as it moves. Angle of attack changes continuously. It is definitely not just about flapping up and down. For a long time, this limited the possibilities of building such machines, while with recent technology it seems possible.

This complex movement also restricts the maximum speed possible, as even small birds cannot beat the wings more than about 80 times per second. The fastest birds, such as the white-throated needletail, may reach 105 mph (168 km/h) in horizontal flight that would not be impressive for an aircraft.