I belted something big passing FL310 on descent once.
Blood and guts all down the side of the 737. Didnt think
a bird could survive with that little oxygen.
Just like the Aztec's of Mexico and South America...you adapt to your surroundings.
Birds, the feathered winged variety, (not especially the mini-skirted female human types) do likewise.
PS:
The mini-skirted female types do as well...sorta.