This is a type of parrot, found, as the name implies, in Howandaland. This parrot is referenced briefly in Moving Pictures as a possible solution to the vexing problem of adding a soundtrack to the clicks. Alas, it is very good at picking up swear words, and moving pictures on the disc has not yet progressed to include Roundworld referents to movie genres such as blaxploitation, modern urban crime, or Eddie Murphy. So the promising idea is shelved.
Norwegian Blue, anyone?
The Howondaland Green parrot may be a reference to the real world African Grey Parrot, known for its uncanny ability to remember hundreds of words and create simple sentences.