What specific feather coloration is the definitive identifier of a Kea when it flies or stretches its wings?

Answer

Brilliant, unmistakable patch of scarlet or bright orange under their wings

The brilliant, unmistakable patch of scarlet or bright orange under the Kea's wings serves as the most striking and definitive identifier when the bird is in flight or stretching.

What specific feather coloration is the definitive identifier of a Kea when it flies or stretches its wings?
birdNew ZealandParrot