Re: Birds in an Airplane

In an aeroplane full of birds, whether on the ground or in the air, the 
weight of the ‘plane and birds  will not change if the birds take flight. 
When the birds are flying their bodies and wings are pressing down on the 
air below them, which presses on the air below that and so on creating a 
downwards push against the floor of the ‘plane. This results in a downward 
force equal to their weight. 

You might like to try this for yourself if you can get hold of a sensitive 
set of scales, a box and some small objects like feathers that take a long 
time to fall. Weigh the box with the feathers settled on its floor then 
shake it and weigh it again as the feathers are falling. Does the weight  
change ?