Galahs are highly socialised and live in large groups. I certainly want to believe they take pleasure in flight, and I love seeing them fly above the Brisbane River where I live but I am drawn to observe they are also probably subject to social pressure like flocking behaviour, peer and dominance establishment, and threat of exclusion. Reduction in stress hormones would be normal in an animal conforming within it's group and not being bullied or put under stress. Still there's a determinism in poo testing I like. It's pretty black and white.

Also, these were presumably cage bred. Not sure I'd generalise from this cohort to the wild.

More work to be done I'd say. The evidence of crows and others repeatedly gliding and swooping from roof ridge to eves and back again suggests they ideate beyond some sense of purpose in flight, doing repeated orbits up and down, on and on, and it looks playful. They do similar compex things not flying very clearly playing (riding frisbees in the snow), which definitely look play like, so it seems reasonable to assert the flight which simply displays an ability to fly with no other purpose is done for pleasure as much as any other reason.

I’m reminded of this D.H. Lawrence poem:

Self-Pity

I never saw a wild thing sorry for itself. A small bird will drop frozen dead from a bough without ever having felt sorry for itself.

Do humans enjoy walking?

I suspect there is also a physiological effect here. We know that exercise in humans has effects on mood and emotional wellbeing. I would have liked to have seen the authors attempt a control where they induced an equivalent level of aerobic activity without flight (although I must admit, I have no idea how that could be achieved in practice).

Fish gotta swim Bird gotta fly Man got ask why why why