Consuelo, I don't think Mr Guthrie would like you quoting him like that.

Anyway - back to the matter at hand - I spent most of my childhood in lovely tropical Darwin. We had mango trees in our backyard, and as a consequence we had a lot of fruitbats in the yard too (they're also known as flying foxes). The point is, another variation on 'mad as' is "Mad as a fruitbat;" I'm not sure whether this was meant to mean angry or crazy, but when they're squabbling over fruit, they certainly sound annoyed... Might also be a play on the idea of 'batty' meaning crazy.