This presumably began as a survival trait, since even an extremely hungry bird would find itself inconvenienced by a nasty localized tornado. From there it possibly became a secondary sexual characteristic, like the plumage of birds or the throat sacs of certain frogs. Look at me, the male says, flapping his wings lazily in the canopy of the rain forest. I may be an undistinguished yellow colour but in a fortnight's tone, a thousand miles away, Freak Gales Cause Road Chaos."
(Interesting Times, Terry Pratchett)