Over in the Aust/NZ song thread, a 28Sept posting of a song about Cockie Bell's sad demise in the WA wheatbelt, mentions :

“…..Cocky / Cockie arose in the 1870s and is an abbreviation of cockatoo farmer.
This was then a disparaging term for small-scale farmers, probably because of their habit of using a small area of land for a short time and then moving on, in the perceived manner of cockatoos feeding…..”
A.N.U. Meanings and origins of Australian words and idioms

https://slll.cass.anu.edu.au/centres/andc/meanings-origins/c


R-J