So he is responsible.......

[William Cloud Hicklin]

Let'as also remember that the ability to fly does not necessarily mean the ability to fly at any altitude one likes. Most birds and early aircraft, and all bats, couldn't manage the 5000 meters or so required (obviously Thorondor's Eagles had wings like a U-2....). Just like aircraft in the pre-jet age, the way to handle high mountain ranges was to go around them.