Noun
flightlessness (uncountable)
The condition of being flightless.
Also, in cooler temperatures heat is lost more rapidly through wings, thus the circumstance favors flightlessness. Source: Internet
Due to its outward similarity to the razorbill (apart from flightlessness and size), the great auk was often placed in the genus Alca, following Linnaeus. Source: Internet
This species had no innate fear of human beings, and their flightlessness and awkwardness on land compounded their vulnerability. Source: Internet