G'day,
Pasted from the MacQuarie Dictionary (very comprehensive Aussie dictionary) CD ROM:

cocky [2]
Colloq.
-n.
1. a cockatoo, or other parrot.
2. a farmer, esp. one who farms in a small way.
3. a mouth like a cocky's cage, a mouth which is unpleasantly furred, as a result of sickness, excess drinking, etc.
-v.i.
4. to follow the occupation of a farmer.

And that's official!

Cheers,
Alan