[Yardstick]

But as you were moving into position with your camera you startled a bird who flew up into the tree and ever so slightly altered the direction that it fell.

[Durus]

It is unlikely that the asmostpheric disturbance of bird wings would overcome any other atmospheric conditions which already exist. Regardless it would seem that you are already changing the thought experiment with additional parameters. The simple fact is that not all observations change what is being observed.