Beneath Ceaseless Skies - The Moult by Christopher Rowe
Merton did not answer because Soliver's jibe had struck truer than he could know. The Moult attacked more than the body. Flightlessness was followed inevitably by madness and then total emptiness of the mind, if the disease was allowed to run its course. Most Kin afflicted as he was killed themselves long before that point though or were killed by others in pointless battles the madness caused the afflicted to seek out.