Regarding this Cecil colum:
http://www.straightdope.com/classics/a3_144.html
I would like to point out that airplanes do have an “open window” while in flight.
You can take a look at it here:
(scroll about halfways down to Main Outflow Valve)
Pressurization is maintained by pumping “bleed air” from the engines to the cabin which replaces the air exiting through the MOV.
This may be, of course, old news. It is just that this column was linked to on a thread discussing something else and it linked to the column which made no mention of this fact. The thread is question:
This means, according to what I understand of Cecil’s column, that a flying pigeon would reduce the weight of the plane (a passenger sitting on another’s lap wouldn’t, of course 
)