How to get rid of unnecessary objects in NLA?

(2.7) The NLA Editor refers to a number of objects … such as, the upper and the lower beak of a cartoon bird … that do not (now) have any actions or such associated with them, and that never will. When the little bird throws his head back and opens his mouth to sing a cheery note in the Beautiful Land of Youthville, that’s done using an armature and actions. But still, here in the NLA editor, I have tracks for the beak-parts which I can’t get rid of.

What, exactly, causes an object to have space in the NLA editor (assuming that you didn’t expressly add it), and, how can you remove them? Can you re-order the objects more conveniently?

Ping …? Anyone?