Flightlessness

Also, in cooler temperatures heat is lost more rapidly through wings, thus the circumstance favors flightlessness.

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.

This species had no innate fear of human beings, and their flightlessness and awkwardness on land compounded their vulnerability.