Winged Beasts, a squandered resource?

[Lalwendë]

In the real world the only 'fell beasts' you find are sheep and the occasional hiker in a cagoule, so in that respect the term makes me laugh.

Bringing back up the quote Nerwen posted:

A creature of an older world maybe it was, whose kind, lingering in forgotten mountains cold beneath the Moon, outstayed their day, and in hideous eyrie bred this last untimely brood, apt to evil. And the Dark Lord took it, and nursed it with fell meats, until it grew beyond the measure of all other things that fly; and he gave it to his servant to be his steed.

Tolkien makes it clear their origins are unknown, but that they had been around in more ancient times, and had gradually died out apart from in isolated areas. They sound as though they could be nocturnal creatures (a little like bats?) and they are carnivores. They can also grow to a huge size if they are bigger than any other flying creature - presumably including both Eagles and Dragons?!