GW_04
The question originally asked by disco_air was what happens to the weight of the aircraft, not what happens to the energy exerted by the birds. Lets look at your argument for a moment to point out what I am trying to say. If we had a planeload of passengers seated in the cabin. They aren’t exerting much energy because they are seated. Now imagine all these same passengers now suspended from the ceiling of the aircraft by individual ropes (not around their necks). The only thing keeping them attached to the ropes is the considerable energy they are now exerting holding onto these ropes. The weight of the aircraft hasn’t changed but there is a hell of a lot of calories being burnt by everyone on board compared to when they were all seated. As you should be able to see the energy being exerted by the birds isn’t relevant to this question, as it doesn’t affect the weight.
