That depends on whether you consider the species undergoing the change part of its own environment. All it takes is change in the morphology of one of the members of a population to change the direction of selection. You also have to remember that there will be no time in the lifetime of a species where there are no selection forces in action.
"Recall, as some other poster on this thread pointed out, that there are all kinds of concomitant changes to lungs, bones, genitalia, what have you that all seem to go together in a package in the birds.
That poster has a penchant for creating strawman versions of evolutionary processes. Both feathers and pneumatic bones existed in dinosaurs before they developed flight. As far as developing a stronger bone structure to support larger muscles through reinforcing the rib cage, Archaeopteryx flew without that bridging and the fusing of clavicles into the 'wishbone' started in dinosaurs before flight.
There is no reason to believe that all the features we find in modern birds had to develop simultaneously. Although modern birds rely on all the features they have this is to be expected, evolution has the tendency to reduce or change in function features with marginal use, but flight does not need all of those features as can be seen in the other organisms which can fly, and those features can be attained through incremental modification.