We fly because birds do.
This is one of those hypothetical statements that is difficult to prove or disprove.
The earliest man was definitely inspired to fly because he saw birds flapping its wings and flying.
But then human beings do lots of things that do not naturally occur in nature.
Two examples … first, we use wheels for locomotion. Think about it … wheels are the most ineffective tools for locomotion in the wild. And unless you consider tumbling weeds as the source of inspiration, there is nothing equivalent in the animal or the plant kingdom.
Second, animals do not blast into outer space. We do.
So, to think that there would be no flying machines is there were no birds is stretching the theory of inspired by nature a bit too far.
However, nothing prevents us from taking inspiration from nature.
Of course, birds are not the only things that fly.
Insects do too.
And they fly in swarms (to be fair to birds, some species of birds fly in spectacular swarms too – Watching more than 60,000 Starlings flying in formation is closest thing to nirvana.)
Flying in swarms is the next big thing in aeronautics.
Imagine a bunch of kids gone trekking with the school. Your daughter is one of them. You are a worried mother when no one returns. They are lost. A search and rescue team is launched, but not just an isolated helicopter or two. A swarm of tiny UAVs (60,000 of them) take off and spread across the forest and within minutes the trekking team is located. How wonderful is that!
At first blush this seems too complicated. But let’s see what the rules of a swarm are.
Rule #1: Thou shalt not collide with anyone. Duh!
Rule #2: Every member in the swarm cannot be controlled from a central location, but the swarm itself shall be controllable from a central station.
(This reminds me of Chaos theory, where simple rules generate complex patterns.)
Experiments are being conducted by universities (Harvard, University of Pennsylvania), companies (Boeing) and in countries (Switzerland) on UAVs to develop and perfect swarming technology. Human beings are getting there!
The next step, of course, is to implement swarm technology in passenger aircraft. While the larger passenger aircrafts are not required to perform aerobatics and will not fly in close configuration, the attraction is to utilize the flying space optimally. Currently there are mandatory vertical and horizontal separation constraints. Aircrafts armed with swarm technology could communicate to each other and taking necessary actions to utilize space optimally. This should be good news for airlines that anticipate heavy passenger traffic in the future.
Stretching the concept further, we can now easily imagine a 3 dimensional traffic highway for flying buses and cars, a scene straight from Star Wars.
But why stop at birds and insects. There are other animals too that fly. Bats fly using echolocation to get to their targets and avoid obstructions in their path. This is fundamentally different from swarms, but achieves the same end by an entirely different technology. Bats’ brain is also wired to distinguish between the reflected ultrasound from an insect and transmitted sound from another bat, another perfect technology to implement in UAVs and manned aircraft.
Coming back to birds … eagles soar on thermals. I have seen glider pilots following the eagles and staying aloft for hours. Dynamic soaring that extracts energy for flight by crossing air masses at different velocities is used by birds. Radio controlled gliders already exploit this. It should be only matter of time when this is exploited in UAVs. The required technology should be able to detect thermals and relatively moving air streams. UAVs designed for Public Safety (or spying) could stay aloft with minimum energy expenditure.
There is much we can take from nature. The future of flight is limited only by our imagination.
 Visit http://www.youtube.com/watch?v=XH-groCeKbE to see swarms of starlings
 Boeing Demonstrates Swarm Reconnaissance with Unmanned Aircraft http://boeing.mediaroom.com/index.php?s=20295&item=1886
 Drone Swarm: Networks of Small UAVs Offer Big Capabilities http://www.defensenews.com/article/20130612/C4ISR/306120029/Drone-Swarm-Networks-Small-UAVs-Offer-Big-Capabilities
 Dynamic Soaring http://en.wikipedia.org/wiki/Dynamic_soaring