So they actually did try shooting the eagle sequence, where Superman is messing around in the sky when he meets one of those friendly midflight eagles that you don’t run into very often, and they loop and dive around each other in close formation, illustrating the beauty and poetry of flight or whatever.
I figured they would have cut that sequence very early on as obviously impractical, considering how difficult it was just to get the guy credibly off the ground in the first place, but the Making of book informs me:
“The flying unit was now working with some natural-born experts: a golden eagle, two Lanner falcons, and a Saker falcon, which were being used to film a majestic sequence of Superman soaring through the sky with an eagle. The Saker falcon was the one finally used and the scene went well; conditioned to fly toward the lights and then return to its trainer’s arm, the bird performed beautifully.”
The amazing thing about that postcard from Pinewood is that they were still having open-casting aviary auditions in February 1978, when it was way too late for them to be dicking around like that.