Kakapos are, according to the late Douglas Adams, "the world's largest, fattest and least-able-to-fly parrot".
Mark Cawardine adds "Strangely, not only has it forgotten how to fly, it also seems to have forgotten that it has forgotten how to fly. Legend has it that a seriously worried kakapo will sometimes run up a tree and jump out of it, whereupon it flies like a brick and lands in a graceless heap on the ground."
Look out for a picture of a kakapo humping Cawardine's head, as Stephen Fry looks on. I can't make it link to the thread.
The Kakapo (Strigops habroptila) is classified as critically endangered on the IUCN Red List. In January 2012 the total global population was 127.