Never met any birds in cloud but one sad bird story that I read of comes to mind.
The wings of the Razorbill are, for some reason which the experts cannot determine, very slowly decreasing in size.
To compensate for this they have to fly faster and this means larger breast muscles to increase the flapping rate. Increase size of breast muscles puts up the weight and thus the wing loading which requires more speed and bigger breast muscles for faster flapping, and so on and so on. The experts did not offer a prediction as to when the poor thing would finally be grounded like the penguin.